Wilkinson's do a nice range of bunny toys for a reasonable price - some of their gnaw blocks are around about £1.
Try your local pet shop - ours sell the gnaw sticks (basically tree branches minus leaves) for 50p and the bunnies love them.
If you have access to an apple tree the rabbits will adore the branches off them as they gnaw the bark off and this helps their teeth.
Balls. Preferably animal toy ones rather than a tennis ball that the fluff will come off. Possibly the hollow plastic golf balls. I wouldn't use a proper golf ball as they are packed solid with elastic and if the rabbit manages to break it open he/she could get injured (my dad and I dissected (sp?) a golf ball once - the speed with which it practically exploded once we'd opened it was amazing!)
Toilet roll tubes (make sure no paper or glue left on the outside) stuffed with hay keeps them occupied - and fed! (kitchen roll tubes cut in half are the same size)
Clean plastic flower pots, various sizes, they'll toss around the hutch/run.
Some RUers leave cereal boxes for them to play with BUT make sure they can't get stuck
Going to more expensive toys you can get the all-weather tunnel type things, but as said these aren't cheap. Rabbits like tunnels.
Best thing to do is pop into your local pet shop/hardware store eg Wilkinson's and similar and have a nosey. Don't feel obliged to buy; if you are asked say you're looking for a friend.