Check the body painting tribe.

krylolan has a new product -
it's supposed to last all day
they told me it was about to
be introduced last time I was
there at the SF store. worth
checking out if available - it
was used at the last olympics.

There are also water based products

Ben Nye - Liquicolor body paint
Kryolan - AQUAcolor and a formulation premixed
for an airbrush... jetcolor or something like that

^^ those are the best of the older products.
I'd reccommend mixing with a sealer product for
body painting with an airbrush. (except jetcolor)
these are not waterproof tho they hold up to
moderate sweating

graftobian and merhon have products
also, but perhaps the formulations aren't
quite as refined. Still useable.

kryolan available here in san francisco
you can look it up in the web or ask if
you have any questions

there are alcohol-dissolved products for
more permenance, but they are a little
much to reccommend for large areas.

I do use kryolans' alcohol dissolved
cake body paint for zebra stripes when
conditions mean I'll be sweating.
but it's a pain to work with. You
can see in my photos, the zebra
in hooves has been pulling a cart in
a hot outfit, but the makeup hasn't
moved a bit...