Apple has provided a web app directory for the iPhone and iTouch. You can browse applications by Most Recent, Most Popular, Alphabetical, and Staff Picks. I'm adding a section on the left of this blog page to provide you with links there which you can use even when this post has rolled off the bottom.
I noticed that some apps that I've seen listed elsewhere are not included. This is probably due to the flakiness of those apps: i.e.: too buggy or too hard to use. Hopefully the app I'm working on will make it into Apple's web app directory! It should show up under "Most Popular" ... ahem... cough... :)
It's not ready yet! Hopefully it will be ready soon.