I just got my iPad a few weeks ago, and have been tearing out my hair trying to learn how to sync it with school. Right now, the apps I'm testing out are:
GoodReader
The support for this app is great. Every time I've corresponded with the developer, I've gotten emails back within, and I'm serious, 20 minutes. That's from 8 am to 2 am, it's like they never sleep. I like that they've added annotation settings, but at the same time, I thought it was going to be like, click on the highlighter or pen color, highlight. Instead, it works more like...select the chunk of text, a thing pops up, and you get to select whether to highlight or underline or whatever. And adding notes leaves a tiny little dot instead of something like a sticky note, which I guess is cleaner, but not as convenient, ultimately. The program is excellent for what it's meant for though. I use it to load my current reading material from my biology classes.
Noterize
Love/hate relationship. It can't handle loading a ton of pdfs or ppts like GoodReader can, but I have a stylus (the Targus one, which works very well, by the way, and is cheaper than all the other ones that look like that), and can just highlight or doodle right onto the screen. This is my go-to app most of the time, specifically in my Anatomy class, where my teacher posts powerpoints. I save them as 2 per page pdfs, put them in Dropbox, load them into Noterize, and I just annotate right on top of them. Perfect for keeping up with the teacher, and much more efficient actually than printing them out 6 per page onto real paper, and trying to see details, etc.
Evernote
Free app. Love this app on my computer, for some reason, don't love it as much as I should on my iPad. I use it for my Zoology class, because it's all copy-down type lecture, and I don't want to pay for Pages or another office suite app until I've decided on which one. A new Note can hold my lecture's notes (with tabs, although not like, pretty nested tabs, which is what I'm wanting). I don't type on the screen. That sounds absolutely horrific. I use the Apple bluetooth keyboard. There's no lag, and it's super comfortable. Afterward, and this isn't most efficient by a long shot, I load up Word on my computer, and retype the notes with the pretty bullets, and load them back onto Dropbox/Goodreader. Although the plus side of that is I get to refresh my notes, ergo learning them a little better.
I also just got Notes+ and Notify. They seem neat, especially with Notes+'s zoom in feature for handwriting, but I've tried that for my Statistics class, and it was laggy and buggy, and just nowhere nearly as efficient as pen and paper. I gave up using my iPad in there, and just grabbed my old notebook.
That was long...hope it helped!