A definition of decent really depends on what you want to use it for. If you want to websurf, send email, do word processing and other basic windows tasks, then you can probably find something refurbished in your price range. Probably not anything new however.
If you want a laptop to play current generation games on take your $600 and save it, or look at building your own desktop. You won't find a current generation laptop for that price.
My Dell CPxJ cost me about $600 refurbished. It's a good P3 laptop but the 8Mb video card really limited it to playing older games, and the lack of a OpenGL driver for the chipset really limited the older games that could run on it. But for a basic laptop it would do everything you want but play games or other graphics intensive tasks. Also with refurbished laptops, depending on what type you are looking at, accessories are easy to find and fairly inexpensive.
One word of warning with refurbished laptops. I bought a good model but ended up with a lemon. Before I gave up on it I basically doubled the purchase price with money spent on repairs. A friend of mine got the same laptop from the same reseller and didn't have any trouble with his.
I ended up getting a loan and buying a new laptop with a warranty for the duration of the loan. I'm buying peace of mind, but that's all insurance is 99% of the time. It's the other 1% that it pays for itself.
If you can tell us a little more about what you are looking for in a computer we can be more specific.