Booked our flights yesterday. Used to be that it was cheaper to book at last minute but these days you generally need to book in advance for cheaper tickets. Yesterday was the last day for booking cheap flights for May and June.
We went with a cheap budget airline and there are somethings you need to be aware of.
The flights we booked were advertised at £10 per person one way, but once you've added check-in costs and 'checked' luggage the flights were £25 per person one way. You can save money if you only have cabin luggage as you can then check in free and don't pay for baggage. We saved money by booking using an electron card, otherwise expect to pay another fee.
The terms and conditions bit of the website explains all the costs. http://www.ryanair.com/site/EN/conditions.php
Be wary of booking the right dates and that they don't clash with anything else as to change the flight date involves paying the whole cost of the flight again.
The airline also offers you cheap travel insurance but we found it cheaper to go to a price comparison website and it cost us about £7.98 for 2 people.