Windows only: We've featured a desktop torrent searcher before, but it only searched one site. If you want multiple tracker searching with seed and peer information, Torrent Magnifier runs on your desktop as a standalone program or a Windows gadget.
Torrent Magnifier provides basic search functionality over multiple popular sites, such as BTjunkie, Mininova and Fenopy. It orders the results by highest number of seeders, as well as providing leecher information — but not much else, like number of validations or the size of the torrent. You can, however, go straight to the torrent's page by clicking the link next to the torrent name. It's nice to have around if you're not too picky about the size of your torrent, or pretty confident in your torrent-choosing skills — otherwise, if you're going to have to go to the site anyway, you might as well use an online aggregator like Torrentz.
Torrent Magnifier is also available as a Windows gadget that works in the same way, as well as a Firefox/Internet Explorer search provider and an Internet Explorer accelerator. All iterations are free downloads — the desktop program is Windows only, the gadget is Windows Vista/7 only, the search provider requires Firefox or Internet Explorer 8, and the Accelerator requires Internet Explorer 8.