http://sjs.co.nz -- when I was looking about a month ago, there was 37 jobs with an average time of 10 hours a week at $25 an hour. They were all sorts: coding eCommerce, website maintenance, Wordpress development etc.

(to search, type 'home' then find 'IT/Computer' in the classification drop down)

Generally I find it has a better range of casual/part-time or even full-time than Seek/TradeMe.