There are quite a number out there (at least 8!) that do the job, but it was difficult to sieve/test through so many when the new site was going live in a very short time, and it was then that I stumbled upon Chris Cagle‘s excellent article:

The Definitive Guide on WordPress Syntax Highlighter Plugins

The article gives a comprehensive review of 8 different code syntax highlighters that work for WordPress 2.6, including (in alphabetical order)

• Code Colorer by Dmytro Shteflyuk
• Google Syntax Highlighter for WordPress by Peter Ryan
• Highlight Source Pro by Christian Knoflach
• Snippet Highlight by Roland Rust
  
• Syntax Highlighter Plus by Fred Wu (with matt, Viper007Bond, mdawaffe)
• WP-Chili by Andrea Ercolino
• WP-Codebox by Eric Wang
• WP-Syntax by Ryan McGeary

The plugins have then been ranked in terms of their overall rating in ‘colouring/coloring abilities’ (with colour screen-shots for comparison included!) and their ‘ease of use’, where WP-Chili came out top in the colour rankings (which is what Chris Cagle is using, and he has helpfully provided what he uses on Cagintranet Web Design) but Syntax Highlighter Plus was #1 for ‘ease of use’.

I found the whole guide extremely helpful, and have now ended up using Syntax Highlighter Plus for WP Snippets – it did help that it was ranked #1 overall! However, given that Andrea Ercolino has updated WP-Chili since the review, I really might look into changing over!

If you are looking out for a good WordPress plugin that highlights code in colour/color for WordPress 2.6, then The Definitive Guide on WordPress Syntax Highlighter Plugins is definitely the article that you would not want to miss reading. To be fair, not every plugin has been updated recently (at least two are from 2007, and the most dated plugin in the list is Code Colorer from May 2007) but nevertheless, it is still an excellent guide worth archiving!