Quoting t_maia
Given the choice between Ryanair and easyjet I'll always prefer to fly with easyjet. Easyjet simply has the better service and you don't have to pay extra for each and everything.
I am afraid in the UK you do have to pay extras with Easyjet. £8 per checked bag each way, a surcharge for payment regardless of what type of card you use (debit cards being the cheapest as £2.95). Food on board can be pretty expensive too. Better to buy snacks etc. at the airport.
I have flown with both Ryanair and Easyjet and didn't see much difference between the two other than Ryanair charge around £4 for payment by debit card.
I have to agree though that Easyjet have a really good service, no frills, get what you pay for and in my experience are rarely late and I have flown with them a zillion times.
A train to Stansted from London Liverpool street will cost £19 or £17.20 if you book via Easyjet. The Gatwick Express from London Victoria costs £16.90. Another option is National Express buses, they service all airports from all over UK. An example fare is London Aldgate to Gatwick is £7.30.
Hope this helps, if you need more info just let me know including the dates you are travelling as it can make a difference.
Re Stonehenge, you could take a look at Viator.com, they do several day trips to Stonehenge from London including sights such as Bath, Oxford and/or Windsor or a self guided trip to Stonehenge only for £33 which takes just 5 hours (includes coach tickets and entrance fee)
[ Edit: Edited on 08-Aug-2009, at 13:59 by baluba ]