First off I'll post with the thought you'll be using the 64bit version of Windows 2008.
I would go for an Intel Quad core processor or dual Xeons and use an Intel motherboard.
For memory go with 4 gigs unless you'll be running database intensive apps then go with at least 8gigs. Memory of choice for me is GSkill.
Use SCSI drives, at least 5, in a raid 10 array for redundancy and best performane.
Whatever you company currently uses for backup will work fine.
I haven't had any problems with any hardware so if you buy top of the line components you be sure it will last you a long tme.