some folks rear the hornworms to adult moths (as well as some other caterpillars). Pick them off the tomatoes and feed them older foliage that I don't mind picking off. Great biology experiment for kids. Just release the adult moth miles away from your garden.
The other use Future that I found is for finding scorpions; a big problem in Arizona and probably other deserts.
Caution: don't look into this light; requires special UV goggles.
Upon doing a little more research into the black lights, I discovered that these are UV lights. The best deal and most powerful mag light I found is here: http://cgi.ebay.com/Ultra-Violet-41-UV-LED-BlackLight-UV-4104-Flashlight_W0QQitemZ120429723288QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1c0a2bbe98&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A570|240%3A1318|301%3A1|293%3A1|294%3A50
other uses: Scorpion hunting, locating pet stains, money checking, credit card checking, criminology, oil-mining, mineralogy, archeology, surveillance, chemical probe testing, security inks, document checking, biology, medical applications, chemistry, food checking, water pollution detection, body fluid, Urine spot, Insect Detection, Minerals Hunting, Automobile Air Condition Fluid Leaking (Freon). Police use it for scanning the crime scene.