There are a couple of good events coming up in March.
March 19th - Ramble Into Spring, McKendree University, Lebanon, Illinois. The university hosts a 5k, 10k, and a 10 mile run, all starting together. This race is a bargain at $12, especially with many races charging $40 or more these days. The 5k course runs through town, while the 10 miles takes you out throgh the cornfields. http://www.mckendree.edu/StudentLife/ramble2011.aspx
March 26th - Tracks n' Treads, Off-road biathlon, Southern Illinois University - Edwardsville. This is an trail biathlon that starts with a 5k run over the university cross-country course and a 9-mile single-track mountain bike race over the challenging course on the SIUE campus. This race is hosted by the Metro Tri Club, the same guys that put on the Pere Marquette Trail Run each December. http://teamgodzilla.org/index.php?option=com_content&view=article&id=9&Itemid=9