My best advice for someone looking to buy their first acoustic is to visit your local instrument store and actually get a feel for some of them. You may not be able to afford the one that you like the most there, but you will at least get an idea of what style suits you the best. Just because a guitar sounds great and has a well-known name on it, doesn't mean it's going to feel "right" to you.
Most local stores (especially The Guitar Center) are VERY customer friendly. You can go in there and just sit down with any of their guitars to see how they sound/feel. Find something you like and then ask the guys there what is comparable in your budget.
I bought my first acoustic online but only after spending a lot of time in my local stores first.
Edit: You can't really go wrong with a solid top Washburn for a starter guitar. They make some fantastic ones for $300, give or take. I own one and I have a couple buddies who have been playing for 15+ years on Taylors, Gibsons, etc. One plays gigs and he said he'd have no problem using my Washburn on stage. But again, get what feels good and sounds good to YOU.