I dislike CSI NY and CSI Miami, so I can only answer questions about Vegas --
They use Streamlight Scorpions as their "personal" flashlight that is carried on each one's vest.
They use Surefire M4 Devastators in most episodes, however during season two about half of the episodes had Streamlight Ultrastingers.
I've seen every episode of CSI Vegas thus far and have seen an Inova X5 only once, what looked like a rechargeable Brinkmann Maxfire (once!), a UK 4AA LED light once, and a Maxabeam several times.
The funniest thing is in one episode you see them holding a Maxabeam in a cave, but then when it cuts to what they're looking at from behind it appears they're using a Surefire M4 Devastator.