The Small Cuts website has an article on the percentage to hit chances in Arty Conliffe's Crossfire. Crossfire, as you may know, is one of the more innovative rules sets to come along. It uses no rulers, and has no real turn sequence.
Canvas Eagles is a set of free wargames rules for WWI Dogfights
S Scale is the railroad scale that most nearly approximates the 25mm - 28mm figure scale. Unfortunately, until recently it has been rather obscure, difficult to find at even the best stocked hobby store. This website has a vast list of S scale resources.
The Illustrated History of the Roman Empire website is just that -- a neat historical site with loads of pictures and interactive map. There is lots of fodder here for historical wargamers.
Rex Hurley has written a set of free wargames rules for playing Last of the Mohicans with 25mm - 28mm wargames miniatures. The rules are relatively simple, and include statistics for all of the main characters, such as Hawkeye, Uncas, Chingachgook, Magua, et. al.
There's also a page of pictures for inspiration.