First things first, do not under any circumstances go for a beige box (i.e. a server you have built yourself). While I'm sure you have the capability to build a system, you wouldn't get the 4 hour response time or next business day warranty like you would if you went with a major manufacturer.
I would suggest you take a look at some of the HP servers. Look around in the ML300 range, or if you want a rackmount server, the DL300 range. The most popular HP server at present is the HP DL380 G5, a powerful rackmount server which gives you scope for expanding in the future. For your data redundancy requirement, you can add a RAID array to the server (I would suggest a RAID 5 array, configured on a minimum of 3 hard disks) which will protect you from a single hard disk failure. If your data is very critical, you may want to purchase 4 hard disks - configure 3 as a RAID 5 array, and the other as a hotspare (so the array will instantly fall over to it if one drive in it fails). The disks you'd want to use are HP's 2.5" 15k SAS drives.
You would need to look at what server-software you want the server to run too. I would suggest, unless there is a reason why you cannot (such as third-party software incompatibility) you go with Windows Server 2008. Standard Edition has Active Directory, IIS Web Server etc., but if you just need Web Serving capabilities, check out Server 2008 Web Edition.
Let me know if you have any questions,
-tigermatt
