I know that personally I would be more than happy to test any Alpha or Beta quality addons for WotLK and I doubt I am the only person on these forums.
That being said I thought it may be a good idea to make a thread where people can post Alpha and Beta quality addons for WotLK. Designers or really anyone for that matter, feel free to post links to your test version addons here. This is not for pre-existing "working" addons, but you can by all means post test versions of pre-existing addons. if you want a list of "working" addons for WotLK that is a different thread please refer to http://elitistjerks.com/f32/t29033-wotlk_beta_-_working_addons/.