Twitwall - a place to post longer tweets, in fact you get a rich text editor, embed code, upload files, and people can leave comments which will appear on Twitter. Another option for longer tweets is tinypaste, or using twitterfeed to auto-tweet stuff from shorttext or publi.sh, or an even a more robust solution like Tumblr or Posterous.
At the moment I’m posting longer tweets using Friendfeed messages, and then getting my FF msg feed auto-tweeted via twitterfeed. Issue I have found so far is that you can draft a FF msg with only so many words, but you can extend this if you draft in Notepad and cut n paste your message in the box, but when published, only an excerpt appears in Friendfeed without the choice to read more…whereas the whole post is displayed in FFtogo (Friendfeed mobile). BTW-you can also post a FF msg using m.hellotxt.com
[UPDATE: I no longer have to use twitterfeed to auto-tweet my Friendfeed messages, has Friendfeed has this available in your settings page, under Feed Publishing]
Twitblogs - a place for longer tweets similar to tweetwall. It has a rich text editor, drafts, embed code, see previous posts, comments…you can even search twitter or use as an alternative twitter interface (which has a nice URL shortner box)
I’m really impressed with Twitblogs, but I’m hesitant to use something when I’m not sure how long it will be around (I’ve been burnt before)
What’s holding me back at the moment is that it doesn’t render that well on my phone like existing Twitter mobile sites, or email posting would be good. They have some strong forums, so time will tell.