You can get it almost anywhere (online, Apple Store, etc.). It's very good at burning different types of media to different formats, and it's never failed me. That said, it won't burn encrypted media (just a head's up). It's easy to use as well. I think of it more as a complement to Handbrake than as a replacement.
It's worth noting that Toast is commercial software, not shareware or legally downloadable -EDIT - without paying -/EDIT - . Your local Mac retailer should have it as well.
I'm off for a bit, but it might help others to answer your questions if you mention exactly what you want to use the app to do - DVDs? What? Because, to me, HandBrake is more of a ripper, and Toast is more of a burning app.