It has some pretty advanced features, since it's been around for a while. DropMP3 is supposed to be fast enough to rival commercial software. AudioCatalyst for Mac is probably very good. I've never used it. It costs money.
Most people seem to like it.
It works from the command line, but if you're using Linux, that won't be a new concept for you. Add Grip to the equation and you'll really be cooking with gas. Xingtech sells an MP3 Encoder for Linux. But I bet the free stuff is better. National Geographic Magazine has no qualms about publishing photos on the web, and neither should you.