Warning: don't buy the Nyko Intercooler if you end up buying one. Those things will slowly kill your 360. I had gotten a new 360 and had an intercooler with it so I put it in (This was about a year or ago X|) after about a month I started getting red rings occasionally starting up the console...My 360 also got into disc killer mode and broke my Halo 3 and Guitar hero 3 X|. (There is a program, which should still be up, where if your disc is scratched by the 360 you can get a replacement for about 10 or 20$. But it only covers certain games, I had my Halo 3 replaced and I had to buy another copy of GH3)

It can also depend on where you live too. If you live in places like Arizona with high temperatures it may do good to buy a reliable intercooler or make sure your 360 has as much ventilation as possible. If you live up in usually cold places you shouldn't have to worry to much about an intercooler. For precautions you could also probably sit it next to a fan or if it's cold outside by a window to keep it cool other ways.

Oh, I almost forgot X|. Yes if you use some intercoolers like the Nyko one it will void your warranty. If you have a model recent enough they may have a little prong in the middle of the power input, If you try to put an intercooler with a wrong design, it won't fit.