Transolution works great on a PC, but it crashes sometimes and our translators have to save often.
On the Mac, if you don't have Snow Leopard, LocFactory Editor is a nice option, but not upgrading to Snow Leopard wasn't an option, so we've stopped using it.
We're currently using Open Language Tools, which works great on Linux and a Mac and recommend it to all our translators. It also has some nice XLIFF validation.
