Are you doing a singer/songwriter kind of thing, or are you playing acoustic in a full band setup? Will you need to plug a microphone into it along with an acoustic guitar?
Genz-Benz is a good brand of acoustic amp. I have a Trace Acoustic that I really like, although I'm not so sure that they're still in production. Fender has a pretty good variety of acoustic amps although I can't speak for their quality myself. Even Behringer has a line of acoustic amps that I've never heard but they're definitely affordable.
As far as features, you'll need an XLR input with phantom power if you're planning on either micing your guitar or singing along with it. EQ options are good to have, more than bass/mid/treble. Either sweepable mids or a full-on graphic EQ are desirable. And a notch filter is a must-have. This allows you to dial in a frequency to be heavily attenuated to fight feedback problems at any resonant frequencies of your instrument or the room you're in.
Other than that, built-in reverb is a good thing to have since it really sweetens and softens your guitar and/or voice.