Twitter Gadget is a great app for accessing Twitter, even if Twitter is blocked (like it is at my district).
Twitter Gadget is an app that you can use in iGoogle, GMail or as a stand-alone app. It is very easy to use and works well. I actually like using it in iGoogle over the Twitter home page.
It's free and the site has easy instructions and references on how to use it.
TwitterGadget in iGoogle:
TwitterGadget Stand-alone in browser:
It's a great resource and I use it even when Twitter isn't blocked.
(If you use a Palm Pre+/Pixi+ I recommend Twee as a great Twitter app for webOS)
Any other great Twitter clients that get around Twitter being blocked?
TweetDeck and Tweetdeck's web app also work if Twitter is blocked and are both very powerful!