I've got 2 120 gb SATA Hitachi 7K250, the only time i hear them is the "meow" and the occassional spin up (my computer isn't silent, but with a Supersonic Silencer 400, a Panaflo 92M (at slow speeds), and the default Lian-Li 6077 fans, and artic silencer for the graphics card, it's still pretty quiet). So if you don't mind the occasional "meow" and spin-up and want blistering fast speeds, they're not too bad. Since they've been out for awhile, the prices on them should be a lot cheaper (I don't know if that's the case where you live).
-my 2 cents
