For those not initiated, a pen tablet is a computer interface, just like a mouse or a keyboard. With a tablet, though, you interact with the computer by using a pen stylus on a flat board hooked up to your computer, usually via USB. The tablet tracks the pen’s coordinates and moves the pointer on the screen accordingly. When you touch the tablet with the pen, the mouse clicks. When you drag, the mouse holds its click and moves along with you. It requires a bit of getting used to but is amazingly intuitive once you grasp the concept.
Modern tablets also interpret how hard you’re pressing and which side of the pen you’re using. This is incredibly useful in digital painting and illustration work.

I got my Wacom Graphire4 pen tablet about two years ago and I still use it almost every day. This is my second Wacom; my first my mom got me when I was in junior high. It used a serial port and I’m sure would work perfectly today if I still had a computer with that connection.
Mine is the blue version with a 6″ by 8″ surface area. The model also comes in white and with a 4″ by 5″ area.
I use it mainly for Photoshop work and Flash animations. In fact, I’ve gotten so used to it, I can barely work with either of those programs without it.
It connects to the computer with an attached USB cable. Higher models from Wacom interact wirelessly with bluetooth.
The pen it comes with includes the normal plastic nub tip, plastic eraser on the other side, and two buttons about where you put your thumb. They are programmable and work well set as double-click and left-click.
The Graphire4 tablet features a scroll wheel and two programmable buttons. Higher models feature more buttons and more scrollers. The buttons work well for going backwards and forwards in Firefox, moving between frames in Flash, and undoing and redoing actions.
Besides the ubiquitous pen, the Graphire4 also comes with a mouse. The mouse uses the same tablet functionality as the pen, so operation can be a little awkward. When you’re working with your mouse at an angle that’s not parallel with the tablet, a straight horizontal line to you is interpreted by the tablet as a diagonal line. It takes some getting used to, but ultimately isn’t as good as a normal mouse.
The pen works well, without any noticeable lag, even with multiple heavy programs running. There’s 512 levels of pressure sensitivity, which is enough for you to not notice any lack of smoothness. Painting in Photoshop with varying pressures produces the exact flow it would in real life.
The screen on the Graphire4 is also removable, so you can lift it up and put stuff underneath it. Mine has stickers.
It works well on PC and Mac with the included drivers. It’s also bundled with some light software, useful if you haven’t the latest creative suite.
Some specs from the Wacom site:
Tablet size: 278(W) x 263.8(D) x 18(H) mm
Active Area: 150.8 x 208.8mm (6″X8″-A5 size)
Resolution: 2032 lpi (0.0125 mm)
Reading Accuracy: ±0.5 mm
Pressure Sensitivity: 512 levels
Report Rate: 100 pps
Weight: 860g
Cable Length: 150cm
Interface: USB
Final thoughts? Very, very good. I bought mine back in the day for 200 something, and it looks like its price hasn’t changed much, even though Wacom’s come out with new models since. I guess there’s a high resale value, so that’s good. I don’t think there’s much else I could want from it.
http://www.wacom.com/graphire/6×8.cfm