Replying to External hard drives

Well, i just reached my 500 gb of internal memory and have a few projects coming up pretty soon here. Used the searchbar a bit, didnt really find much useful info. I need at least 500gb, but preferably 1TB or 2TB. This will be used for my Imac. Dont really wanna break the bank, but defiantly need something reliable. What are some good ones people like? I have heard some things about rugged or somthing. Help me out quick! I need something right away. +K for help