How best can we market template sites? (sites that sell templates) Are there any template directories? Are niche markets/forums etc where we can market them?
Before you worry about the "where," think about "to who." Choose your market, and then look for outlets that are influential to them. I'd suggest forgetting the generic web template market, and look for a niche not overly saturated (there are just too many free templates out there to the general audience - like those here on DP). For example, you might specialize in templates for band websites, or model portfolios, or small business sites, or photography / design / art portfolios, etc.
Try exchanging with a few high PR directories. Start from there. Then go find your market. Who are most likely to buy your templates? Are they more corporate or personal? Evaluate first.
sites like that are everywhere nowadays .. I had one site like this and sold it cuz it was too hard to promote .. unless you offer something trully special.. it will be hard to promote
If you don't have the first idea about how to market a site to a specific niche, a good idea may be to do some reading on traditional marketing and advertising, as the same principles apply on the internet. It will help immensely both now and in the long run. jhmattern touched on this a little bit, in my opinion, by pointing out that you're looking in the wrong direction initially.