Cheap airline

[twasadark]

This is for my European flisties - what's a reliably cheap airline I could use to fly between London and Rome? I'm trying to decide whether I want to take advantage of a British Airways flight to London next spring, but I want to continue on to Rome after a few days and I want to see whether it would be cheapest just to go from LAX to Rome rather than make the stopoff in London.

Thanks in advance!