Motorola Xoom (10.1'') should be available in April.
LG is launching a tablet, branded T-Mobile G-tablet, also 10'' I believe.
Dell Streak 7 should also be available sometime soon.
Acer is supposed to launch a tablet but not sure of the details.
Asus tablets in a variety of form factors should be available around April to June I think.
All of the above are Android with full market access. Archos 101 and Archos 70 are cheap but decent tablets that come WITHOUT access to Market but there is a hack that enables full access to Google apps as well as market (but of course thats at your own risk and definitely not official).
On other OS front, Blackberry Playbook is supposed to come soon. HP/Palm have an event on Feb 9 and should be launching at least one tablet.
For the screen size, one thing you must also consider is weight and portability. Take a look at this article for example where the author says he ditched the iPad for the Galaxy Tab because of the higher portability of the Tab.
http://gigaom.com/mobile/why-i-just-dumped-the-ipad-hint-size-matters/
iPad is heavy in the sense that it requires holding with both hands and big, i.e. not really something u can slip in a coat pocket. 10'' tablet s are not very "mobile" and I personally like 7'' tablets but everyone's usage scenario is different.