I use Reaper. If you have any questions as to the awesomeness, flexibility, and robustness of Reaper, go search for "Boojum" on iTunes and listen to a preview (my Boojum is the one with the giant curved cactus on the cover -- I don't think there are others but it's been a while since I checked).
Now, even as professional as the recording sounds I was doing my source in 16-bit 44.1 wav format because we recorded to my Fostex VF-16, and then exported the tracks to Reaper. I now have a Presonus interface ($400 or so) into a laptop via firewire, and I am doing source tracks at 24-bit 96 khz. The next Boojum outing will probably sound even better. I mean, I can hear some flaws in the mix but those flaws are due to source limitations and engineer (my) ignorance. I'm not trying to show of my band, just demonstrate that Reaper can put out a professional-quality recording. I both mixed AND mastered from Reaper.
License for Reaper is well under $100. And it absolutely whip's the llama's ass.
Cockos Incorporated | Company. No, I do not work for them. I am just blown away by the quality and value of their product.
And I do believe they have a Mac release.