Duff-Man says....if you are more specific about what hardware you have, what you are looking for (capacity), where you are located, and if you have a budget to spend (including installation if you are not qualified to d.i.y. - it's not easy in most laptops) you'll get better responses for your situation.
In general, drives are the same wherever you buy them - the warranty is from the drive manufacturer..so you are probably looking for best price I assume. Check all the usual online places if you are in the USA - NewEgg, OtherWorld etc etc etc....I would suggest looking over at DealMac.com as they list all the latest deals out there....oh yeah!