For keying out the genus of North American ants, one of the easiest keys to use can be found in:
Wheeler, George C. and Wheeler, Jeanette (date unknown) Insecta: Hymenoptera Formicidae in Soil Biology Guide (Daniel L. Dindal, Editor). John Wiley and Sons, New York, 1227-1295.
The following internet discussion groups are available to anyone at no cost. The first group listed, ENTOMO-L, is for professional entomologists. The second group, BUGNET, is for teachers and students. Professional entomologists monitor communications on BUGNET and promptly answer any questions. You need to contact the listowner for instructions on how to join.
A seemingly unlimited internet source of entomology information can be found at the Entomology Index of Internet Resources. Specific instructions for joining ENTOMO-L and BUGNET can also be found at this location also.