More and more Job sites are putting RSS Job feeds on there sites. CW Jobs have there feeds organised by type Permie or Contract and then by skill which works well for the techie's like me.

UKLug is a site that aggregates jobs from 19 other sites and allows you to search using keywords and then use your RSS aggregator subscribe to your search. An example search: +london +chef

If your in the job adverstising business and don't have an RSS feed on your site then you had better add one quick!