The following is a list of web apps/sites that I use on an almost daily basis on my phone, some of them replace installed applications for me and others simply augment them. I use my phone constantly for web browsing, just ask @alishahunsaker. Visiting the links provided on a standard computer/browser might not take you to the mobile optimized site, either load up this page on you phone or scan the qr codes to go directly there.
Google Reader (http://www.google.com/reader/i, QR) - Google has done a great job of keeping me addicted to Google Reader, their mobile app is fast and easy to use, great for reading when you are away from your computer.
Google Product Search (http://www.google.com/m/products, QR) - This page has a barcode scanner button, so you can scan barcodes and then search online w/o crowding your phone with the "Google Shopping" app, "ShopSavvy" or "CompareEverywhere" which all do the same thing. Not as comprehensive as the installed apps, but it has worked for everything I've needed.
Twitter Mobile (http://mobile.twitter.com/, QR) - Twitter's basic mobile site has been refreshed for newer, more capable phone browsers. Even though I have an installed Twitter client, sometimes I need full access to the entire feed. If I haven't updated Seesmic in a while, I don't always get the full feed of updates.
Gowalla Web (http://m.gowalla.com/, QR) - Gowalla's android app is still in development and has a few bugs to workout (it has gotten a lot better since). The mobile site is fairly reliable and one of the better looking sites/web apps out there. It is integrated with the device's GPS to guess where you are and lets you checking/post to twitter and add new venues. It's still not perfect and occasionally the device can't find me and thinks I'm miles away from my actual location.
Google Docs (http://docs.google.com/docs/m, QR) - Currently the mobile interface allows you to view/edit Spreadsheets, and view Docs and Presentations. Any other files you may have uploaded to Google Docs are visible and will download to the device when clicked. Overall the interface is clean and similar in nature to the full Google Docs experience for browsing files. The only problem I've found is with viewing forms is the browser gets stuck in a refresh loop and I think they should give you an option to view the form or the results spreadsheet.
Facebook (http://touch.facebook.com/, QR) - The mobile site works just as well as the installed (Android) app for viewing Facebook feeds, commenting, sending message, etc. What it doesn't do is allow you to upload photos, which in my case isn't a big deal. Also, you don't get alerts like you would with an installed app, once again, not a big deal for me because I get emais when that stuff happens. Saves space on my phone, does what I need.
Bank of America (http://bofa.mobi/, QR) - My bank has an app on most platforms, based on their Android app, its a simple port of their mobile web site with some GPS features thrown in for good measure. The mobile site supports viewing accounts, bill pay, transferring funds, location finder (w/o GPS). Haven't used another bank, aside from the American Express Mobile site (which is fairly spartan, but reliable,) so I don't know if any others are doing it better.
Check.in(http://m.check.in/, QR) - This site is in beta as of this writing and aims to solve the problem with "Check-In Fatigue". I've been using it for about a week now, it integrates Brightkite, Foursquare and Gowalla into a simple, easy to use mobile site (after I've logged in and connected to the other sites). I fire up the app, it locates me, I select my location from Brightkite's database of locations, then it attempts to match up with the other services and find the same spot using magic. If a match cannot be found it asks you to select the appropriate match from a list of available locations or to skip the service in question. Once the places have been selected for each of the services, you simply "Check-In" and you are done. This really works much smoother than I described here. Only problem is, you don't know if there are any Foursquare specials, if you've become mayor, if you've discovered an item, etc. This is an efficient way to Check-in, but it removes some of the appeal of each service, so I may continue to use a combination of both.
Others worth mentioning but not used as often:
Ars Technica - http://arstechnica.com/
Bit.ly - http://m.bit.ly/ or http://m.j.mp/
Digg - http://m.digg.com/
Disqus - http://m.disqus.net/
Espn - http://m.espn.go/
Flickr - http://m.flickr.com/
LinkedIn - http://m.linkedin.com/
Netflix -http://netflix.com/mobile
PayPal - http://mobile.paypal.com/
TripIt - http://m.tripit.com/
Google Reader (http://www.google.com/reader/i, QR) - Google has done a great job of keeping me addicted to Google Reader, their mobile app is fast and easy to use, great for reading when you are away from your computer.
Google Product Search (http://www.google.com/m/products, QR) - This page has a barcode scanner button, so you can scan barcodes and then search online w/o crowding your phone with the "Google Shopping" app, "ShopSavvy" or "CompareEverywhere" which all do the same thing. Not as comprehensive as the installed apps, but it has worked for everything I've needed.
Twitter Mobile (http://mobile.twitter.com/, QR) - Twitter's basic mobile site has been refreshed for newer, more capable phone browsers. Even though I have an installed Twitter client, sometimes I need full access to the entire feed. If I haven't updated Seesmic in a while, I don't always get the full feed of updates.
Gowalla Web (http://m.gowalla.com/, QR) - Gowalla's android app is still in development and has a few bugs to workout (it has gotten a lot better since). The mobile site is fairly reliable and one of the better looking sites/web apps out there. It is integrated with the device's GPS to guess where you are and lets you checking/post to twitter and add new venues. It's still not perfect and occasionally the device can't find me and thinks I'm miles away from my actual location.
Google Docs (http://docs.google.com/docs/m, QR) - Currently the mobile interface allows you to view/edit Spreadsheets, and view Docs and Presentations. Any other files you may have uploaded to Google Docs are visible and will download to the device when clicked. Overall the interface is clean and similar in nature to the full Google Docs experience for browsing files. The only problem I've found is with viewing forms is the browser gets stuck in a refresh loop and I think they should give you an option to view the form or the results spreadsheet.
Facebook (http://touch.facebook.com/, QR) - The mobile site works just as well as the installed (Android) app for viewing Facebook feeds, commenting, sending message, etc. What it doesn't do is allow you to upload photos, which in my case isn't a big deal. Also, you don't get alerts like you would with an installed app, once again, not a big deal for me because I get emais when that stuff happens. Saves space on my phone, does what I need.
Bank of America (http://bofa.mobi/, QR) - My bank has an app on most platforms, based on their Android app, its a simple port of their mobile web site with some GPS features thrown in for good measure. The mobile site supports viewing accounts, bill pay, transferring funds, location finder (w/o GPS). Haven't used another bank, aside from the American Express Mobile site (which is fairly spartan, but reliable,) so I don't know if any others are doing it better.
Check.in(http://m.check.in/, QR) - This site is in beta as of this writing and aims to solve the problem with "Check-In Fatigue". I've been using it for about a week now, it integrates Brightkite, Foursquare and Gowalla into a simple, easy to use mobile site (after I've logged in and connected to the other sites). I fire up the app, it locates me, I select my location from Brightkite's database of locations, then it attempts to match up with the other services and find the same spot using magic. If a match cannot be found it asks you to select the appropriate match from a list of available locations or to skip the service in question. Once the places have been selected for each of the services, you simply "Check-In" and you are done. This really works much smoother than I described here. Only problem is, you don't know if there are any Foursquare specials, if you've become mayor, if you've discovered an item, etc. This is an efficient way to Check-in, but it removes some of the appeal of each service, so I may continue to use a combination of both.
Others worth mentioning but not used as often:
Ars Technica - http://arstechnica.com/
Bit.ly - http://m.bit.ly/ or http://m.j.mp/
Digg - http://m.digg.com/
Disqus - http://m.disqus.net/
Espn - http://m.espn.go/
Flickr - http://m.flickr.com/
LinkedIn - http://m.linkedin.com/
Netflix -http://netflix.com/mobile
PayPal - http://mobile.paypal.com/
TripIt - http://m.tripit.com/