I started with a 25 gallon one from Harbor Freight. Don't waste your money. I upgraded to a 35 gallon Porter Cable. Still portable, but a GREAT compressor for that size/style/price range. When I moved into my new house, I bought an 80 gallon 220v beast. I love it, but I only sold my portable because I couldn't come up with a reason to keep both.
If you're not ready to go with a big one (read 220v), I'd suggest you buy the best quality, name brand portable you can find. Craigslist is a good idea. The guy that bought my portable got a STEAL on a great compressor with very little usage.
Be cautious with Craftsman, or the Lowes and Home Depot ones, even if they are a name brand (even Porter Cable or IR). Their quality is a little lower, as they're building them for someone who's a very casual user. If you compare a similar name brand unit from a box store with one from a tool specialty store, you'll see a difference in manufacturing, capability, etc.
You didn't say what you're using yours for, but just about anything will run an air impact (as long as you're not hoping to break loose lug nuts on a big truck). Running sanders, grinders, etc, that run constantly will be a bigger demand on your compressor, and will stress the portables out. You can get better service by buying a little better (as described above). Look for the most running CFM, and biggest tank you can get for your $$. PSI isn't as big a deal as CFM. CFM is what drives your tools. Don't pay as much attention to peak CFM--I'm not even sure what value that number has, besides marketing. Running CFM will give you an indication of how long you can run a constant-demand tool like a grinder before you're too low on air and have to give it a rest to let the tank refill. Too small of a tank, or too low CFM, and you'll spend a lot of time listening to your compressor run, but not being able to run your tools, because you have to wait for your tank to refill (which, if you're impatient like me, will seem like hours).
Find the tools you want to use, and figure out which ones have the biggest air appetite. That'll help inform your decision quite a bit.
FWIW, you'll have a hard time painting a car with a portable. Not saying it can't be done, just saying you'd better be a REALLY GOOD painter, cuz it's going to be challenging with that small of an air supply.
To sum it up: You get what you pay for. You can get a good quality 110v unit for around $350 brand new, better on sale or on Craigslist. Look for biggest tank and most CFM you can afford, with a bias to more CFM over more PSI. I don't recommend oilless at all. And, as an added bonus, the better quality will generally run significantly quieter than the lower end units.