No offense, but iSimon didnt do a good job of explaining the info you needed. It really depends on if ur going for new or used. If ur going for new, then just make sure you get a warranty w/ it. Depending on where you live, Gamestop (if you have one in you area) is always the best bet. They offer the best warranties out there. Sony just started doing warranties on them, but Gamestop is by far the best value for the warranties.
Now if youre goin for used, theres alot of variables to think bout. First off, you need to find out if its in good working condition. Gotta make sure it hasnt received the ylod (yellow light of death) yet. Also you need to figure out which version of the ps3 youre gonna get. They start at 20gb (the 1st one that ever came out & extremely rare to find if in great working condition) & go all the way up to 120gb (very few 250gb systems are used). Accessories is another big thing to look into. Make sure it comes with at least one controller. Some people just wanna sell ya the console by itself (no power, a/v cables or controller). It will be great if it comes w/ the box & manual, but both are optional. I prefer to have the box come w/ it, but manual isnt as important. I can find out the lil details online. Also, when it comes to used, esp when you look on eBay, make sure that it comes from a seller w/ a great rating &/or # of items that theyve sold while theyve done business on ebay. I happen to get a great deal on my 60gb system (cost me a week paycheck, but ive been completely happy w/ it, not to mention the fact that the guy was local & was extremely nice & helpful).
Now the optional info: If the system comes w/ games, great! I got a 60gb version used (come w/ both wi-fi & ethernet, which is great). If it comes w/ more than 1 controller, then thats extra awesome on your part.