Couple things:
One, if your MBP is still under warranty, the warranty is void when you replace the hard drive. The only component the end user can replace on the MBP without voiding the warranty is the RAM. You will have no warranty at all on any part of the computer once you open it up to change the drive. If your board or screen or anything else dies in a few months' time, you're SOL.
Two, you need a 2.5" serial ata (SATA for short) laptop drive. Doesn't matter if it's Serial ATA-150 or 300, any SATA drive will work.
Three, get a Western Digital, Seagate, or Hitachi drive. There are no other manufacturers that I would recommend.
Four, get a 7200rpm drive. It is more expensive, and the largest capacity available is 200GB (while 5400rpm drives are available up to 320GB), but it is
significantly faster than a 5400rpm drive, and it has no effect on battery life or heat.
And five, where to buy is going to depend on what country you're in.
www.newegg.com is good if you're in the U.S., and
www.ncix.com is good if you're in Canada.