Forget price comparison sites. They rarely show the real bargains which some airlines offer. (Additionally, some airlines might not honour bookings made through third party 'price skimmers'). Go direct to the websites of the relevant airlines. (Many budget airlines haven't released their summer 2010 bookings yet, so you might have to wait a while).
The three scheduled airlines flying from Gatwick South to Sharm el Sheikh are Thomas Cook
http://book.flythomascook.com/cheap-flights/
Viking
http://www.vikingairlines.com/
and Monarch
http://www.monarch.co.uk/flights
From Gatwick North your choice is either easyJet
http://www.easyjet.com/en/book/index.asp
or Thomson
http://flights.thomson.co.uk/en/index.html
For such a popular destination in August it's unlikely that there will be any last minute bargains. The lowest prices are likely to be those offered as soon as the flights go on sale (which means that you should consider booking now, if possible, or no later than the end of this year).
Chris