This year sees the largest number of airlines operating regular services for many years. I think there are currently 16:
EasyJet (& EasyJet Europe)
Wizzair (& Wizzair UK)
Ryanair
Blue Air
El Al
Vueling
TUI
Thomas Cook
Sun Express
AlbaStar
Travel Service
Freebird
Air Nostrum
Tarom
DHL/EAS
MNG