I use MAMP Pro alongside Panic Coda as a local development test server for my websites beffor publishing to the live server and it works great - plus it gives me the additional benefit of being able to quickly preview my code in a number of different actual browsers, not some half baked web preview window (hello dreamweaver I'm talking about YOU).
If you work on just one site then the free MAMP is probably the best option, however if you work on a number of different sites concurrently then the simple virtual host setup in the Pro version is definitely worth the money.
Recommended.