I would suggest getting an adapter that adds a USB port to your Macbook Pro. I don't know enough to suggest something, so I recommend going to your local Apple store or Best Buy to have them help you in getting an adapter.
Once you have this, there are several computer speakers you can choose from that have USB inputs (check out Best Buy). Or there are a couple studio monitors available that have USB input:
Behringer Studio 50USB - typically $150
Alesis M1 Active 320 USB - $75-100 used on ebay
If you want something better than these, then look for a USB DAC, optionally with a volume control, such as Parasound Zdac or something similar. Then you can choose any powered studio monitor from a pro audio company (such as Yamaha HS5 / HS8, or Adam a7x, etc. etc.).