I had been planning to do this for a while: it’s my first WordPress Plugin! Over at Roy on Magic, I often have to write out decklists and such, so I wanted to have an autocard feature similar to the one used at MTGSalvation. After a quick five-minute search I couldn’t figure out how they did it, so I just wrote the plugin myself. Actual effort was around 3.5 hours, most of it struggling with PHP and Regular Expressions. :p
Details and download are at http://www.roytang.net/wiki/index.php/MTG_Autocard_WP. Hopefully someone else will find it useful.