http://www.buxcomm.com/antennas.htm . I would also check out ham universe at http://www.hamuniverse.com/dipivcal.html . One of my favorites for a good selection of antenna calculators is at http://www.ve3sqb.com/ . If you are a moxon antenna lover be sure to check out http://www.moxonantennaproject.com/ .
If you are looking for some good Ham Antenna Software check out: