I wrote a Python script to get a word cloud of my tweets:

https://farm5.staticflickr.com/4032/4207786266_9e85802af2_o.png

I use Twitter Backup to get my tweets in text file, then run my script to generate a list which you can use on Wordle.net’s Advanced.

If you have a common.txt, that would help to remove some common words in result, but you can remove in Wordle, too.

PS. Twitter only allows you to access last 3,200 tweets, so go to back up as soon as possible! (I lost almost 400 tweets, hope I can get them back someday)