Here are some of Europe's low-cost carriers/airlines.
Please note that this is not a complete list.
If you know of any others, please post.
Albania
Belle Air
Austria
InterSky
flyNiki
Belgium
Jetairfly
Czech Republic
SmartWings
France
Transavia.com France
XL Airways France
Germany
Air Berlin
Germanwings
TUIfly
Hungary
Wizz Air
Iceland
WOW air
Ireland
Ryanair
Italy
Air One
Blu-express
Latvia
airBaltic
Turkey
Corendon Airlines
Onur Air
Pegasus Airlines
SunExpress
Atlasjet
AnadoluJet
Borajet
Netherlands
Transavia.com
Norway
Norwegian
Romania
Blue Air
Spain
Iberia Express
Volotea
Vueling Airlines
Switzerland
EasyJet Switzerland
Ukraine
Wizz Air Ukraine
United Kingdom
easyJet
Flybe
Jet2.com
Monarch