Well, the best way would probably be to write a post in our Classifieds section - many keeper leagues will be looking to replace players during the off-season, or be starting from scratch. Also check occasionally to see if others are looking for teams to join their leagues. I assume that the greatest activity in the Classifieds section will next February and March, but checking in occasionally before then can't hurt.
There are certainly many free keeper leagues around. A lot of those use free services such as yahoo, but just keep track of keeper rosters and any special rules such as salaries manually. I believe sandbox, for instance, also runs free public keeper leagues without any manual book-keeping required, but the number of keepers is very limited (haven't played sandbox in a while, so you may want to check the parameters yourself).
Many keeper leagues use an auction draft format, by the way - you may want to include your location in the Classified if you wish to include leagues with live, in-person auctions.