If you want a slate, I think
Motion
http://www.motioncomputing.com/ and
HP http://h18000.www1.hp.com/products/tabletpc/
are the best. (Of course, you can get a keyboard component that makes it laptop-like.)
If you want a convertible, I think
Toshiba
http://www.csd.toshiba.com/cgi-bin/tais/pc/pc_tabletPcDetail.jsp?comm=CS,
Fujitsu http://www.fujitsupc.com/www/products_pentablets.shtml , and
(probably) IBM/Lenova http://www.pc.ibm.com/us/thinkpad/xseries/tablet/
are good.
Acer http://global.acer.com/products/tablet_pc/ may be okay... but the new ones I've seen seem too heavy for me.
Visit the resources and forums on
http://studenttabletpc.blogs.com/
http://www.tabletpcbuzz.com/ (look at the activity on their forum page to see what is popular)
When the tablets were just coming out, the Toshiba was the most powerful tabletpc on the market... but I heard that it had a disappointingly short battery life. Maybe things have changed since then.
Personally, I like the slate. They are lightweight and have fewer moving parts (hinges may wear down... my M1200 doesn't even have a fan). I think Motion is leading the innovations: view-anywhere option, array-microphones, biometrics.
I suggest you go to CompUSA to play with some of these tablets (e.g. Toshiba, Acer). Franklin Covey used to sell and have an HP on display. This company http://www.alltp.com/mobile.htm offers a 48-hour trial of the Motion. (Learn more about this on the tabletpcbuzz site.)
As a student, you may be able to get a student discount on some of these machines.
My $0.02.