Just about any tablet PC ought to work for this. I used a Thinkpad X61 Tablet for several years, and after it broke I bought a Thinkpad X200 Tablet. A typical Windows tablet comes with software called "Windows Journal" which works well for taking notes, and can print to PDF using PDFCreator. I also purchased a program called PDF Annotator, which lets me hand-write notes on top of any existing PDF file.
When I was first considering buying a tablet, I had trouble deciding between the slate type and the convertibles that come with a keyboard and a swivel screen. I decided on a convertible, and I'm very glad that I made this decision -- my tablet also functions perfectly well as a standard laptop, and I keep it in laptop mode about 90% of the time. A straight-up tablet with no keyboard would be almost as expensive, and would be considerably less useful.
