Low cost airlines

Here's a list of low cost airlines websites.

Note: Before booking a flight check the luggage allowance and excess fees, most of the time it is cheaper to book a flight a bit more expensive and not pay excess fees.

Travel cuts
STA Travel
Ryanair
EasyJet
BMIBaby
FlyBMI
Virgin Express
SkyEurope
Lufthansa

Australia
Cathay Pacific Airways
Qantas
Jet star
Tiger Airways (certain Asian countries as well)
Virgin Blue (domestic only)

Austria
Austrian

Belgium
Aerlingus
SN Brussels Airlines

Czech Republic
Czech Airlines

Denmark
Scandinavian

England
(all european airlines go there)
These are the principal one:
Ryanair
EasyJet

Finland
Finnair
FlyMe
Blue1

France
OTU Voyages
Nouvelles Frontieres

Germany
Germanwings
Air Berlin

Greece
Olympic Airways
Aegean Airlines

Hungary
MALEV

Italy
Alitalia
Mediriana
Air One

Nedeerlands
Transavia

New Zealand
Air New Zealand

Norway
SAS Braathens
Icelandair
Fly Norwegian
Scandinavian

Poland
Wizz Air

Spain
Spanair
Iberia
Air Europa

Switzerland
Swiss Airlines

Thailand
Thai Airways