Busted drives happen. In general I get pissed if they last less than 3 years, and I'm surprised and pleased when they last more than 5.
DealMac is pretty good, check froogle.google.com as well; you're looking for a 2.5" hard drive. 5400rpm or faster is probably nice, but any speed will do. Seagate, Maxtor, Western Digital, and a few others are pretty reputable brands.