I checked GeSHi today and saw there had been lots of updates since the last time I updated my Syntax Highlighting plug-in for WordPress, SyHi. There was even support for retrosexy languages such as 6502 and 68000 assembler, and zxbasic--which prompted me to immediately update my plug-in so that people can post code snippets for Commodore 64, Nintendo Entertainment System, Amigaaaah or ZXSpectrum!
So with this new version, there's support for the following new syntaxes, in addition to the existing ones: 4cs, 6502acme, 6502kickass, 6502tasm, 68000devpac, algol68, autoconf, autohotkey, awk, chaiscript, clojure, cuesheet, e, ecmascript, f1, fsharp, gambas, gdb, genie, go, gwbasic, hicest, icon, j, jquery, lb, logtalk, magiksf, mapbasic, mmix, modula2, newlisp, objeck, oxygene, oz, perl6, pf, pike, postgresql, powerbuilder, pcre, purebasic, q, rpmspec, rsplus, systemverilog, unicon, vala, xbasic, and zxbasic.
The full list of supported syntaxes can be read at my SyHi page.
You can download the plug-in from its WordPress.org page or from its github repository. If you have already installed it, you don't need to do anything: it will prompt you to upgrade at some point when you log into the WP admin area--the upgrade process is absolutely straightforward and you just need to press the upgrade button! :-)