In my opinion, there aren't really any great hotels around the airport. There is the Brisbane Riverview Hotel (formerly the Powerhouse) which used to be alright - not sure what it's like now though. I'm sure somebody will know. I think you can usually find cheap rates of wotif.com.

The airport itself isn't actually that far from the CBD though - a calm 20 minutes on the train. Are you renting a car?

If you're going to Australia Zoo, you could consider catching the train from the airport to Roma Street station, which is underneath the Holiday Inn (haven't stayed there). The Australia Zoo bus (which has some stupid name, like the "croc coach") leaves from the transit centre beneath the hotel.

Or, if you were looking for something a little bit more upmarket, you could catch the train to Central Station (one stop before Roma Street), abovewhich is the Sofitel (formerly the Sheraton - nice, but a bit overpriced I think). Then it would be a matter of catching a cab (if you're lazy), or a train (one stop), or walking (15 minutes) to the Roma Street transit centre to get on the bus.

Of course if you're not into bus travel (like me) and you have a car, the Riverview is probably the best option.