There are a few new "tablets" coming out mid 2011, to rival those already on the market... All depends on your budget & what you are looking to do with it...
Most of the speed of these are similar 1.0GHz to 1.5Ghz, so check for storage / apps / compatibility with other devices (connectivity) / battery life... don't write off the android based tabs due to number of apps... they are increasing everyday...
Tabs I know of - iPad2, HP TouchPad, Samsung Galaxy tab 10.1, HTC Flyer, Motorola XOOM. Blackberry Playbook... as mentioned above, CNET is great for reviews... but google around & check out the users forums... owners are very honest when it comes to reviewing their use of these...