Guinea Pig Bedding

There are all kinds of options out there for guinea pig bedding...with one major exception. Cedar is NOT to be used under any circumstance; its oils can cause serious diseases in all kinds of rodents and rabbits, so don't use it for any of your small animals!
Now, I know I'm going to get comments about this, but I do use pine shavings. I do not, however, use the "fancy" shavings from pet stores, or the rough-cut pine intended for livestock. I have never had any health issues with pine; my seniors have been living on it all their lives. If you do use pine, just make sure it doesn't have scents added to it, and don't use livestock bedding as it can contain large chunks that guinea pigs can chew on, not to mention other stuff that can be ground into it.
Fleece is an attractive option for guinea pigs, as it is comfortable and washable, and can be made or cut to fit any cage. I put Prescott on fleece when his bumblefoot wasn't healing quickly enough; all I have to do is wash it out every 2-3 days. It's warm and snuggly...much better than the newspaper he had been on before!
You can also use aspen bedding, Yesterday's News, or Cell-Sorb, but be prepared to pay for it. Aspen is relatively inexpensive, but the other two are not, especially if you have a LOT of guinea pigs like I do.
Whatever bedding you choose, make sure you keep the cage clean. Sometimes I change bedding out twice a week, depending on how "productive" my piggies are. If you walk in the room and the cage smells bad to you, it's beyond time to change it...and imagine what your guinea pigs are smelling living inside it! Keeping the cage clean is even more important if you have long-haired breeds like silkies or Peruvians. Ammonia and solid waste buildup can lead to respiratory problems, and the waste can get matted into your guinea pig's coat and feet. Keep everything clean and it will save you a lot of headache (and vet bills) in the future!