Dell is the BEST in my opinion, I've got over 30k in gear from them. I'd recommend not going with Celeron as noted earlier. If it's for video editing make sure you have at least 512mb of ram, possibly 1 gig. Another good option if you could affort it would be SCSI drives.
One of the best kept secrets would be:
http://outlet.dell.com
http://outlet.us.dell.com/Dispatcher... XXA&tgtSeg=B
or
http://outlet.us.dell.com/Dispatcher... XXA&tgtSeg=B
I don't recommend getting a Dimension. Instead, go with their business-class Optiplex or Precision systems. Dell refurb systems come with a same as new warranty.
Happy shopping! Check out the links above.
Brad