If you are only gonna pay $500-600 for a motor, you will only be getting a D series motor probably. You can pick up a D16Z from a 92-95 Civic Si or EX for about that price. 125hp (more like 130), revs to 7200, and Intake lobe VTEC. Good motor that willl last you a long time and give you great gas mileage. Try
www.thepartstrader.com for an engine that is used and cheap. Guys that do swaps sell them there all the time for really cheap (I have seen them for 200 dollars and less before).
And by the way, american cars aren't the dark side. Most importers just don't like them cuz some of them are fast =)