http://www.motioncomputing.com/products/tablet_pc_le17.asp
That is the tablet pc that I use, and I highly recommend Motion Computing.  They make the best tablet pc's and that is the only thing that they make, but they are expensive if you buy new.  The tablet/screen is great and can be used as a graphics tablet, as well as for note taking.  I use Microsoft OneNote for all of my note taking now and I love it.  The handwriting recognition is excellent and all of my handwritten notes are fully searchable and organized.
I haven't used photoshop on the tablet yet, but have been using corel draw and it is certainly easier than using a mouse for drawing.  The only thing that I don't like is not being able to use keyboard shortcuts without pulling up the on-screen keyboard.  My tablet has bluetooth and can connect to a bluetooth or usb keyboard easily, but I actually just carry it around as a slate only.  
Depending on what kind of processor/ram etc you are looking for, the Motion LE1600 goes on ebay used for about $300, the LE1700 goes for about $900 used, or $1300 new on ebay.  The LE1600 and 1700 look almost identical, just a few differences, like the 1700 comes with 
windows vista and a intel core 2 duo processor...
Look around on ebay and craigslist if you are going to buy one.  I found mine on craigslist and got a really good deal.