Great advice above from Greg and Aaron. Spend a little extra and get a smooth playing one.
My acoustic is an Ibanez electric/acoustic. Off the top of my head I can't remember the exact model, I'll have to look. It wasn't too expensive and I bought it used off of eBay. It sounds good played as is or plugged in, whichever you prefer.
When buying, read the reviews on guitars and look for "ease of play". Like Aaron said, those cheap ones will have too much space between the strings and fret boards and will kill your fingers.
Speaking of killing your fingers, when you first start you will hate it until you build up callouses.
Once you learn the basic chords (A, C, D, E, G) you can play damn near any song with the right rhythm. There is a cool app called Tabs that shows you chords of any song you can think of. Some will be easier than others obviously.
A good website for similar material is called Guitar Tabs.