Diphenhydramine HCL (Antihistamine) works for me on stings--Wasps, bees, ants and scorpions. Then dab a little Cortizone-10 on the site(s). I typically drop a couple before I go out to mow weeds too.
Edit: Oh yeah, my "kit" also contains Neosporin Cream, some Band Aids and a bottle of New Skin...