Toshiba makes great Tablet PCs! I have a Portege M400, and recently the M700 has been released. It has a great feature set and for a decent price. Any decent tablet PC will probably be around $1500-$2000, and these fall in that range. Check them out:
Toshiba Tablet PC List
Among new features on the M700 are: Wireless N support, touch screen without digitizer (can use fingers), and Core 2 Duo CPUs
One thing I would recommend: get the bare minimum RAM that you can from Toshiba and upgrade yourself. All you have to do is pop out the keyboard and the RAM slots are right underneath. They rape you with RAM and it's a very easy thing to upgrade. You might consider that for hard drives, too.
Lenovo's are solid, but I think Toshiba's are a bit more stylish and cost effective. There are other brands to check out. Also, visit http://www.studenttabletpc.com
. Lots of information for students using tablets!