A post to the CS-Nation comments (thanks HomeLAN Fed and HLFallout) by Valve's Erik Johnson reveals plans to release more content for Counter-Strike Source before the end of the year:

We're working on porting some more of the classic maps right now, currently de_prodigy is in the works. We'll be releasing this as quickly as they are completed.

We're also working on one original map, which will begin internal playtesting this week. This still means we have a fair amount of work to do on it.

We're also working on two updated player models.

Most of this is scheduled to be released in the December timeframe.