Basically, check the manufacturing date and ensure that you are not buying any Xbox360 from before 2007. Try to get one that was made as recent as possible to reduce the probability of the infamous "Red Rings of Death".
I bought mine back in late 2006 because of DOA:XBV2, and as I mentioned a few months back, I had to replace it thanks to that "Red Rings of Death". Since then, I've been using the Xbox360 pretty damned often to check if it will crap out on me again, but it's working great so far. My new manufacturing date is actually 05DEC2006, but trust me, if you must buy a new one, get it as recent as possible.
Most importantly... DO NOT MOD IT.
Unless you have a technofreak that can fix Xbox360s for free, modding it will void the warranty. Also, do not buy any Intercoolers, especially if it's NIKO. They may cause a burnout in the Xbox360. Almost all accessories are not Microsoft supported, so be careful. I'd draw the line at protection for the controller.
I'm operating mine in an environment that has 70% dust and 90-100% humidity and no air-conditioner, but so far it's still good... FYI: the Xbox360 sucks air from the base if you're standing it on the side, so elevation might be good (but not necessary). I don't have mine elevated, although it's standing on the side to save space. Beside my Xbox360 is the old Xbox and my 2nd-hand PS2. (Reminds me... I stashed the Super NES along with the Final Fantasy III cartirdge below the table I mount the three consoles on.)
Personally, the only game I'd like to play on PS3 is "Soul Calibur IV" just because of Darth Vader... I just can't bring myself to buy the Xbox360 version because the thought of playing as Yoda doesn't rock my world. Well, at worst I always have nubile DOA girls to play with that the PS3 doesn't have...
Anyway, I'm thinking of buying the Settlers of Catan boardgame.
