Bedding

The traditional bedding for guinea pigs has always been wood shavings. But over the years the care for guinea pigs has changed. We now know things that we didn't know before. Wood shaving are dusty and can cost quite a bit. They can cause health problems. Even some wood shaving are toxic to them.
I have listed the worst to best below. There are many different opinions for bedding.

Cedar is VERY Toxic-
The problem with cedar shavings stems mostly from the oils that give it its aromatic scent. Cedar has been shown in studies to be hazardous, causing chronic respiratory conditions in mammals. Some animals are even allergic to cedar, and can develop severe skin rashes or more severe respiratory conditions.

Corn cob-
It molds fairly quickly.Guinea pigs have been know to eat it. Particles can get stuck on food.If ingested and the guinea pig drinks water, it swells up and does not break down, creating a potentially serious blockage.
Pieces can get lodged in the genital/anal area causing medical problems.

Straw-
Straw is completely unsuitable as bedding. It does not absorb urine, and the hard stalks can cause serious injuries

Pine -
Like cedar, pine is a soft wood whose oils give it an aromatic scent. Although there is still some debate as to how dangerous pine really is, many serious owners of small mammals such as guinea pigs, rats, mice and the like will recommend against its use. If forced to choose between pine and cedar, pine is definitely the better choice, but you really should avoid both if at all possible.

Aspen shavings-
Aspen shavings are completely safe as bedding, but the con about this bedding is it is more expensive than cedar or pine, also hard to find. A problem with aspen is that it is a hardwood, and it has no natural oils to give it a strong scent. Aspen doesn't function too well for odor control, making it that you will have to change the bedding more often.

CareFRESH-
A popular alternative to wood shavings is CareFRESH.
It is made from wood pulp fibers that are too short to be made in to paper. CareFRESH's greatest strength is its odor-control: like most paper-based beddings, CareFRESH inhibits the formation of ammonia.

Yesterday's News-
A recycled paper, pelleted bedding. It comes in regular pellets and soft texture pellets, and contains an odor-controlling agent.

Fleece-
Unlike traditional beddings (wood-shavings, hay, CareFresh), fleece is reusable.