There are lots of options.http://www.amazon.com/Logitech-io-Personal-Digital-Pen/dp/B00006JP23
Live Scribe (requires special paper, available at places like Best Buy):http://www.livescribe.com/en-us/
Of the many people I know who has gone this route for school (including iPad and tablets), they all say it is not worth it and give up. They are to slow and cumbersome to use and in class you end up missing information. Except for Light Scribe, but, the paper is a lot most costly then regular notebook paper.
For tablets like the iPad you have to buy a special stylus, yes.
I have played with them all, and like them; but except for Light Scribe I just do not see them being useful for Chemistry, because in Chemistry you do more then just text and numbers, lots of weird figures, etc.
Even people with the really expensive FULL laptop/tablet PC's (not the simplified iPad like devices), they give up usually and switch regular paper.
But I HIGHLY recommend you you go to stores or find people and really try for a good bit to use the devices as you intend; not just quickly and think "cool". I personally do not own any. I used regular paper with a 4 color pen, and have a cheap auto-feed scanner (you just give it a name and date, load all the pages and hit go). Its honestly much cheaper and just as effective and easy in my opinion.