I bought a used Thinkpad T22 for $400. It works pretty good - the only problems I've noticed are poor battery life, and the left mouse clicker on the laptop sometimes isn't very responsive. With a battery capacity of 17.03 Wh out of the original 38.88 Wh, I get roughly an hour of life with wireless ethernet and a bluetooth mouse. (While browsing websites)
Downsides - No wired ethernet (The ethernet card is $50 or less, wireless ethernet works most everywhere tho so it's rarely a problem). No internal wireless bluetooth/ethernet (Mostly because the laptop is so old). The processor, while 1 Ghz, is a P3 rather than a P-M so it's not as efficient. The videocard is also pretty lacking, although that does mean it doesn't sap the battery life, and it's common for IBM tops. There's only one USB port on the back; on the side would be more convenient. The speakers (like nearly all laptops) aren't that great; but the headphone jack is easy to get to.
Upsides - Much cheaper than buying a new laptop. It's very compact, I was able to fit it in my backpack with at least one textbook and my large binder. It's also pretty light. I was lucky enough to get an abnormally high screen resolution - 1400x1050. Since I'm on 1280x1024 on my desktop, the usual laptop 1024x768 seemed cramped. It also has a "ThinkLight", which is handy if you're using the laptop in the dark...it's a small LED above the screen that lights up the keyboard. The jacks for the sound card are conveniently located on the left. I think it has an S-Video port on the back too, but I've never tried it out; it would be useful for powerpoint or whatever. Volume controls are easy to find in the dark (Up/down/mute).
