The following languages are supported in the lang attribute:

abap, actionscript, actionscript3, 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, gettext, glsl, gml, groovy, haskell, html4strict, idl, ini, inno, io, java, java5, javascript, kixtart, latex, lisp, lotusformulas, lotusscript, lua, m68k, matlab, mirc, mpasm, mxml, mysql, nsis, objc, ocaml-brief, ocaml, oobas, oracle8, pascal, per, perl, php-brief, php, plsql, python, qbasic, rails, reg, robots, ruby, sas, scala, scheme, sdlbasic, smalltalk, smarty, sql, tcl, text, thinbasic, tsql, vb, vbnet, verilog, vhdl, visualfoxpro, winbatch, xml, xpp, z80

(Bold languages just highlight the more popular ones.)