Xtorrent is a BitTorrent client and search tool for the Mac. It was written from the ground up in Cocoa and makes this tool a very native app. Xtorrent comes with a search feature that allows you to find new torrents. By default, Xtorrent looks in ClearBits, Google, Yahoo! for torrents. A quick trip to the preferences allows you to add other sites and enables a search in the PirateBay, which works better than the default searches.
Xtorrent behaves differently than most other BitTorrent clients I have tried. It has a very clean interface that really has all you need in a single window. You can run multiple searches and go back to them at any time before you close the app. You get a good number of results with the default search engines, and you can add your own for better results. The app also allows you to subscribe to torrentcasts, which are like RSS feeds but with torrents.
In my little time with Xtorrent, I didn't find any problems and the experience was smooth. I got OK download speeds from the torrents that I found using the built-in search feature. Xtorrent will impose a 100kb/s download speed limit after 10 minutes of use unless you upgrade to the paid version.