Here's a tour of a new web-based media production tracking and collaboration system called Shotgun. More info and links can be found via Final Cut User, which has a backlog of updates queued.
Another system recently twittered is Shotrunner, which has some QuickTime tutorials. The blog vfx.netzfilter posted some other options found in research Research on visual effects production databases and Random Links - Visual Effects Pipeline Design and Production Databases.
Update: VFX Nexus is another entrant in this niche. "It's specifically designed for tracking shots and enabling collaboration between artists and supervisors, allowing both a clear view of the status of their projects, shots and tasks at all times. This ideology - coupled with report creating, deep search abilities and customized views - is our version of Project Management." Here's a summary:
Update 2: There's a number of newer services that could branch into this niche too, even if they mostly do review and approval: Xprove, CineSync, FilmFlip, PIXSytem, MediaBatch, and MESoft. Let's hope someone does a proper roundup that compares these options and includes other software like Celtx.