I'm with Atlantic Electric and Gas for my Gas and Electricity, and I have just opened up two letters from them this morning. They are thanking me for staying with them (it must be my year anniversary), and to say thanks, I'm being credited £21.25 for my electric account, and £37 for my Gas! (Basically, they are refunding me a month's payment for each).
Also says they will give me more money back for every year I stay with them, and continue to pay by monthly Direct Debit.
Glad I didn't switch now :)