Linux Mint Katya 11 is very smooth and friendly and nice; you'll love it. I'd also recommend AriOS, which is a sweet-ass version of Ubuntu. The two share my laptop hard drive, and I use Ari more than Mint.
It's in the Ubuntu Software Center. I'm in the same boat as you: I use an iMac as my main computer, but my laptop has AriOS on it, which is an Ubuntu derivative. I tried tons of music players before settling on Rhythmbox and Songbird.
Edit: added link to the lovely and snappy AriOS.