Chap Mei is the name of a toy company that specializes in 3 3/4" figures, vehicles and playsets of various styles.
A lot have appeared to try to cash in on the popular "fads" of the time, Dino Valley/Dino Quest features human scientists, hunters and large dinosaurs, and seems to be made to appeal to Jurassic Park fans.
The Pirates toyline, although lacking a Jack Sparrow-ish character, is clearly aimed at fans of Pirates Of The Carribean.
Beast Raider is obviously based on the Masters Of The Universe relaunch.
There's also more generic lines like Wild Quest (animal-based), Extreme Adventures (adventurers/explorers), Wild Arctic (arctic-based explorers), Police Force/Police vs Bad Guyz (police vs criminals) and their longest-running line ever, Soldier Force (sometimes also sold as Freedom Force), which features soldiers and military-based vehicles.
Distribution is iffy. It really depends on where you live... All I can find in my area are repackaged Soldier Force figures sold under the TRU "house brand", Elite Operations, along with some Dino Power ninjas and Extreme Adventures figures. Meanwhile, people in South Africa seem to be able to find all the new stuff easily.
You can find out more on the site and forums here:
http://www.chapmeitoys.com