I got a 120gb one for around £50 (or maybe it was £40..) on ebay - it's just a Vaio rip-off but it hasn't caused me any problems so far. Still, if you want definite reliability, maybe you should get a brand name one.
dabs.com - PC Hardware, Components, Software, Digital Cameras, MP3 Players - this place can be good. Umm... and yeah, get one with high rpm (though I think everything over 5400 is fine, and most of them are).