I want to start out by saying something very unfortunate, but in my opinion, very true: there is no perfect cat litter on the market. There are various types of litter out there, which is one thing I want to cover in this post, but the reality is you need to pick and choose your battles. It won't be too hard to see which battle I'm fighting...
The most common type of litters out there are clay-based. They're cheap, they clump, and cats tend to like them. They are also VERY environmentally unfriendly, as the main ingredient that causes clumping, sodium bentonite, is STRIP-MINED from as deep as 50+ feet into the ground. This material does not compost and it does not break down - this stuff is in our landfills for the long haul. There is also concern that sodium bentonite can be harmful for the cats - they inhale it, and it is on their paws and fur after use, which is then ingested via grooming. There are no proven studies that show it is harmful, but it has also only been on the market for ~20 years - a relatively short time. My guess is that we will start to see studies come out against the use of this material in the future.
Alternative options are not perfect, as I mentioned, but they are better for the environment, which means they are better for me. There are many, but I will just touch on the most common and readily available.
World's Best Cat Litter is made from corn husks. As far as usability and availability, it is very similar to clay. It clumps in a very similar manner, without using sodium bentonite. It's price point is higher than clay litters, but it tends to last for a decent amount of time with regular scooping. The negatives: the corn is likely genetically modified corn, and has been exposed to pesticides and herbicides. It is clearly not organic, and there is no research regarding what kind of remnants of that kind of treatment is still present in the litter. Again, no research does not mean no harm. This is the most similar litter to clay, and cats tend to like it, but it may pose a health risk. Odor control is reasonable, not outstanding.
Feline Pine is made from, shockingly, pine trees. The wood is a natural source, clearly better than clay, but there are concerns regarding pine resin and oils that could remain in the litter and potentially be harmful for cats. Again, no research on this, so no definitive answers. It is pelleted, which does not always please the cats, and is probably my biggest issue with it. When the pellets become wet, they turn into sawdust which can be difficult to scoop out. Odor control is quite good, as long as you like pine trees.
Yesterday's News is made from recycled newspaper. I like the idea, and I would love to support this whole heartedly, but unfortunately it is pelleted as well. The pellets become damp mush when wet, and often you end up dumping the whole box rather than successfully scooping out the waste material. If you are a diligent daily scooper it is possible to use this with success, as long as your cat approves of pellets. As a multi-cat household I found it to be very difficult to stay on top of cleaning without wasting. Odor control is minimal, but if you're scooping often it's less of an issue.
SWheat Scoop is a wheat based litter. It clumps pretty well using wheat's natural properties when wet, and does not have any added chemicals or fragrances. I could not find information on whether then wheat has been chemically treated with pesticides, so that concern still exists. There are reports of insect larvae being an issue with this type of litter (so maybe pesticides aren't an issue), and assumably this would be a problem with World's Best as well, given the crop nature of the litter base. Odor control is decent.
There are other varieties of litter out there, as I've mentioned. There is more information regarding various litters here: http://www.thelighthouseonline.com/articles/natural.html, and an article discussing clay litter here: http://cats.about.com/cs/litterbox/a/clumpingclay.htm. There is also the whole internet, which has opinions too :).
Before signing off on litter speak, I want to briefly touch on flushing and composting. Cat feces should NOT be flushed into the water supply. Many cats are carriers for Toxoplasma gondii, a parasite that can cause disease in mammals, and has been linked to the decline of sea otters on the west coast. While we don't have a complete understanding of what damage this parasite can cause, it's better to play things safe. Please keep your cat poop out of the toilets! As for composting, animal feces can be composted, but NOT into compost used on any edible plants. Composted animal feces can be beneficial for your decorative flower beds and your shrubs, but keep it away from your vegetable gardens and fruit-bearing trees!
I hope that at the very least this post encourages you to think about your litter. And if anyone has ideas for a truly perfect, eco-friendly, cat-friendly, affordable litter that we can produce and retire on, let me know!