I need an acoustic guitar for under $600. I have no idea where to start looking. I don't care if its acoustic or acoustic electric and I'll manly be playing acoustic rock, jazz, and blues. I've been looking at the Takamine G Series EG460SC NEX ROSE Cutaway Acoustic Electric.
And how would an acoustic electric sound through an ac30?
you'll get much more bang for your buck if you go acoustic and add a pickup later. you can get an all solid and very good sounding blueridge http://www.maurysmusic.com/inc/sdetail/35952 or 000 http://www.maurysmusic.com/inc/sdetail/35949

you could get an all solid recording king - not as good as the blueridge perhaps, but i pretty much like recording kings. or you could get an epiphone masterbilt acoustic electric DR-500MCE - while i'm not masterbilt's biggest fan, it is all solid and it sounds it. there are a couple other masterbilts in your price range, too.

rosewood does cost more, but there's some all solid rosewood guitars to be had in your price range:
or for just a few extra bucks

one more worth checking would be this ovation
it's very bassy with the wrong strings, but with the right ones - i'd suggest dr rare pb's - it sounds really good.

an acoustic guitar doesn't sound that good through an electric guitar amp.
I just helped my friend pick out a nice Taylor 110 that sounded fantastic. I'd advise checking out one of those, to be honest. Sounds and plays really excellent.
Jasmine ES33C
Hamer Sunburst Archtop Flametop
Electro-Harmonix Big Muff Pi
Fender Frontman 25R
I have read real good things about Godin 5th avenue, its an archtop and it works great for jazz. blues and to some extent even rock stuff. You can get a Kingpin version that has built in pickup or straight acoustic and add your own pickup. Not sure what they cost...

Another option is either a good Yamaha or Takamine acoustic electric - they have some of the best electronics in the industry. I played a few G series acoustic Taks and wasn't impressed - sounded a bit dull for me - but once hooked into an amp you can make it sound however you want to I suppose.

If you have an electric guitar amp your acoustic will sound muddy through it, but try it and see for yourself. I purchased Marshall acoustic amp and really like the way it sounds with my Ovation run through it.