TwitterGadget is a clean, robust, web 2.0 style client for Twitter, designed to submit status updates to Twitter via your iGoogle homepage, Gmail Account or as a standalone app (website). Using TwitterGadget, you'll get a fully featured Twitter client embedded into Google Wave.

How to Integrate Twitter into Google wave

Create a new Wave and click on "Add gadget by URL":

And paste this URL into the input box:

http://www.twittergadget.com/gadget.xml

and done! :D