I use WP-Syntax for formatting code on my Wordpress blog. It uses GeSHi for language parsing and keyword highlighting. A copy is included in the plugin source so that it is pretty much ready to use out of the box. It supports the following languages:

• abap
• actionscript
• ada
• apache
• applescript
• asm
• asp
• autoit
• bash
• blitzbasic
• bnf
• c
• c_mac
• caddcl
• cadlisp
• cfdg
• cfm
• cpp-qt
• cpp
• csharp
• css
• d
• delphi
• diff
• div
• dos
• dot
• eiffel
• fortran
• freebasic
• genero
• gml
• groovy
• haskell
• html4strict
• idl
• ini
• inno
• io
• java
• java5
• javascript
• latex
• lisp
• lua
• m68k
• matlab
• mirc
• mpasm
• mysql
• nsis
• objc
• ocaml-brief
• ocaml
• oobas
• oracle8
• pascal
• per
• perl
• php-brief
• php
• plsql
• python
• qbasic
• rails
• reg
• robots
• ruby
• sas
• scheme
• sdlbasic
• smalltalk
• smarty
• sql
• tcl
• text
• thinbasic
• tsql
• vb
• vbnet
• vhdl
• visualfoxpro
• winbatch
• xml
• xpp
• z80