Well, an iPod touch will do what you want. Get a slightly better microphone to attach, and you're good.
Or if you want something a little cheaper and easier to use, think about a
$1. You can get recordings off it easily. The battery lasts a good long time. And not only does it record, it can also help you access books from various libraries for the blind (bookshare, NLS, etc). If you're going to spend the money, you might as well get something that can help you with school in multiple ways.