If there's one thing I've learned, don't waste your money on "bunny" toys!
Plastic baby keys are very popular, as are plastic slinkies, whiffle balls, plastic cat balls and plastic baby links (you can buy like 24 of the links at Walmart for $4... look for that package, as there's another brand of the links that's not nearly as good a deal).
Dollar stores (the ones where everything is actually $1) can be good sources of bunny toys if you look around with an open mind. In addition to the various hard plastic toys I've already mentioned, untreated wicker baskets are also fun for bunnies and often found at dollar stores.
Old phone books for shredding and big cardboard boxes (no colored inks) they can "rearrange" by chewing holes/doors in are free and lots of fun.
Tunnels are great too. We love the Ware fun tunnel in 8'' diameter (it comes in 4'' as well but my girls outgrew that by 12 weeks old and they're dwarves) which collapses/can be bent and is hard plastic so it's easy to clean... they also loved their crinkle cat tunnel from Petco (better than the Walmart one, imo, since it's longer - 5' instead of 3', iirc), but I had to throw it out after we moved in with my boyfriend and they got into a pee war with the cats over it (eww!). Another great tunnel option is to get a "concrete form" at a hardware store (they come in various diameters, are 4' long tubes and are made of cardboard so they double as chew-things.
Mine also like the pop-up cat cubes from Walmart, which are pretty cheap and can be connected together (though I'm about to have to replace many of them because they've been chewed so much ><). Their favorite chew toy (that they're actually *supposed* to chew on) is ware willow balls - if you can afford to buy a bunch at once/stock up,
this site is the best price I've found (you can always pick one up at Petsmart first to see if it's a hit or not).
I have a website where I sell stuff for sugar gliders (adorable little marsupials), but I gave Nala and Gaz a page of my store for
bunny-related stuff - if you skip to about 2/3 of the way down the page, I've got some videos from YouTube of bunnies playing with plastic keys and slinkies. A little further down is a picture showing the remains of a decimated phone book - just below that are links to some of the toys we like (the tunnels, for example, though I need to remember to go add the link for the concrete forms). In the picture of their condo at the very bottom, you can see the baby links from Walmart hanging. Gazzles really loves to grab the end and swing it around! I've also got a link to the section in my blog where I built an agility course for my girls - that's a bit pricier and involves some DIY work, but it's TONS of fun to do agility training!