I use a <code2html> tag on my wiki that displays source code as spiffy syntax-colored and formatted html. While it isn't a standard html tag and the cpu load to process the source can be a bit much, it's been quite useful on our site.

The Code2HTML.pm package that does all the work is a single perl module that I adapted from Peter Palfrader's utility. You can see it described on my wiki here. And the Code2HTML.pm perl package is available here.