I've just posted this on the Halkidiki forum on Trip Advisor, and thought it might be useful on here too...

As the UK operators seem to be reducing their hotels in this area, I thought I would see who offered what, and this is what I came up with:

HANIOTI
Ampelia - First Choice & Olympic Holidays
Bella Grecia - First Choice, Thomson & Thomas Cook
Daphne - Olympic Holidays
Dionysos - Olympic Holidays
Elinotel Apolamare - Olympic Holidays
Elinotel Polis - Olympic Holidays
Hilltop - Thomson & Thomas Cook
Hanioti Village - Olympic Holidays, Thomson & Thomas Cook
Lesse - First Choice & Thomas Cook
Naias - Thomson, First Choice & Olympic Holidays
Nereides - Olympic Holidays
Pella Beach - Thomson & Thomas Cook
Renaissance - Olympic Holidays
Sousouras - Olympic Holidays

PEFKOHORI
Aeollos - First Choice
Alia Palace - Thomas Cook
Aloni - Olympic Holidays
Ammon Garden - Olympic Holidays
Anna Maria - Olympic Holidays
Dimitris - Olympic Holidays
Ioli Village - Thomas Cook
Pelli - Olympic Holidays
Tassos 2 - Olympic Holidays

Olympic Holidays seem to have the most presence in the area, particularly in Pefkohori...

A lot of the hotels now have their own websites, and with Easyjet, BA & Ryan Air flying direct to Thessaloniki (although I thin only from London airports) you could always book independently.

I hope this helps, just trying to do my bit to encourage tourism in Halkidiki!

Hope to see you there...