For those of us who want sustainable, environmentally responsible lives, we like to consider all aspects, including clothing.
Think about what your clothes are made of ... when evaluating natural vs. synthetic products, a lot must be considered. Pleather is not as long-lasting as leather, but it's cheap and not made from an animal. Polyester is made from petroleum (=oil!). It also doesn't breathe as well as cotton. Nylon is also made from petroleum, vs. wool made from sheared sheep's fur.
Some people are looking for more eco-conscious clothes and finding new (not-so-new) materials such as hemp, soy, bamboo, and organic cotton. They are long-lasting, durable materials and easy to care for.
Many companies, including Great Lakes Brewing Company, are also looking towards these new fabrics as consumers are becoming more eco-responsible. I've been looking into hemp and soy clothes, and found these options for companies to outfit their staff, or sell to customers. Along with suppliers Kami has found (see comments), these companies are appealing, and their t-shirts don't cost much more than a regular cotton t-shirt.
Onno.com seems to be the best option for wholesalers. They have some good options, and put the prices and quantity available right on the website.
Efforts in Canada has a good selection of sustainable clothes, and offers wholesale prices with no minimum orders.
Bamboo Clothes offers a lot of clothing at reasonable prices, and they say their bamboo/cotton blend are the softest t-shirts on the planet (...mmm... tempting).
Rawganique.com has many styles, and unisex t-shirts range from $16-18 retail. (no new wholesale customers)
One problem is that a lot of these companies are small, to avoid sweatshops and poor quality, so they don't offer wholesale volume yet. The trend is catching on, so look for wider availability soon. Ideal Bite lists several soy clothing suppliers, which seem to be more expensive than the hemp clothes.
Check your label ... are you eco-stylin'?