You can use the AutoCL, which can be found on the WWS site:
http://www.lossendil.fr/serendipity/
Or you can use LoggerHead if you prefer ACE stuff. It also let's you configure in which zone you want to save you combatlog:
http://www.wowace.com/wiki/LoggerHead
Using AutoCL and /combatlog never caused any problems, even combat logs at around 50 MB never caused a drop in WoW's performance. The size was a problem for Windows' Editor though, so I started using Textpad:
www.textpad.com