Matt, the Trane Comfortlink II I mentioned before is probably best deployed when using Trane communicating furnace and AC equipment because they'll all talk to each other. There's also an adapter for regular 24v control which is required for non-communicating gear. I'm pretty sure modules exist to interface with commercial automation systems like Crestron and Control4, but I think it's more stat than I need.

The one you linked to sounds like it may do what you want and work well with your Z-Wave stuff. I'll have a closer look later when I can sit down, I'm kind of in and out at the moment.

For me one of the things I really wanted was a circulation mode for the fan so that I didn't have to leave it on all the time and so that it would come on at other times in addition to heat and cooling cycles.

The EcoBee gets a lot of positive comments as the best stat with wifi and web connectivity available to consumers. It does not have Z-Wave. It does have Zigbee which is currently used exclusively to talk to smart meters to monitor energy usage - which it can use for deciding how to run your AC, etc.