I can certain suggest what to HDs to get but the best thing I do is give you hints on what you should look for.
1. Fast RPM - better access and usually faster throughput.. IDE goes 7200 RPM fastest, SCSI goes 10,000RPM fastest.
2. Cache - Try find one with 512k cache..
3. Well Known brand - never trust a name brand you've never heard of.. With major name brands , there usually comes a better warranty..
4. Get more then you need.. You'll eventually need more HD.. We started out with the 2.16 IBM HDs. We should of gotten a 4GB version of it.. We've been running out of HD on the root and /var/spool/mail partitions..Its a pain buying a need HD and duplicating the old HD onto the new one..
5. Buy more then one HD, its a good idea to have one in storage just in case one blows up..
Don't forget to compress logs (ie. messages, syslog, debug, access_log, etc..) regularly.. You'll start noticing a lag on the system if you let them grow.