For a Mac based solution look at Episode Engine from Telestream
For a PC based solution looks at Carbon Server from Rhozet
Both products will allow you to easily scale up as you output more content.
Both are fault tolerant,
Both offer gridding of transcodes, (jobs are split over boxes/processors/processor cores)
Both produce high quality output.
Both are very reliable.
Both are very flexible in what they offer.
Both get faster the more you throw at them (up to to a defined limit, of course)
Please post back saying what solved your problem. It could help others, and saying 'thanks' is free!
i agree with daniel. episode engine for a mac and carbon server for pc, they're costly but they work. personally i'd go with episode engine out of the two, but that's just because i prefer macs. out of interest what format is the source media?