If you are looking for a job out of LHR or LGW, try to grab the Airport Newspaper (what's the name again?).
If you live near LGW, try the job centre at Ashdown house (South Term, next to the "Tunnel" on the perimeter road, where the CAA bus pick you up too). Most jobs will be advertised but you will also be able to pick a copy of that paper.
In fact a couple of years ago, there was a paper for LGW and one for LHR but they ended merging it into one so both airports will be covered.
Lots of seasonal work with Servisair, Avions on the ground or with the charters as CC.