If you want a PDA just to take notes for college, I say save your money. PDAs with keyboards are fine for occasional note-taking, like at a conference, but they're not very good for day to day use. In college classes, the professor will often draw diagrams, go back and elaborate on earlier points, draw arrows to connect things, write equations, etc., and this is all a pain on a PDA. (Also, as much as I hate to say it, PDA+keyboard combos look terribly geeky -- you'll be the only person in class with a gizmo like this, and you'll get looks.)
TabletPCs are okay, depending on what type of classes you have, but having used one, I'll say that in general they're not that good for taking notes either. You have to write much larger than you would on a piece of paper.
If you really want a practical note-taking device for class, here are three good options:
1) Buy a used AlphaSmart Dana off of eBay, or buy one of the lower priced AlphaSmart devices new. These are essentially portable keyboards with a small display meant for notetaking. The Dana includes a full implementation of PalmOS, so you can run all the PDA apps too. You can just chuck an AlphaSmart in your backpack and not have to worry about it, and the battery life is very good. There is also a company that makes a similar competing device, but the name escapes me at the moment.
2) Get one of the Anoto / Logitech note-taking digital pens. These devices look just like regular pens, but everything you write is digitized and can be uploaded to a computer at the end of the day. The downside is that you need to buy special paper, but even after buying a lot of paper you'll still be well under $300. These devices are small, inconspicuous, and it's easy to do all kinds of note-taking with them, including diagrams and equations.
3) Get a cheap used laptop.
