Asian Bestiary parts 01 & 02.
You might think that it's system specific, but the HERO system has a way of breaking down abilities and stats in a very detailed manner, so it's actually great as a sourcebook not just for Philippine monsters but for other monsters in the region.
I only have reservations about the art of the Philippine monsters, but you have no shortage of monster art online.
In fact, I'd direct your attention to a series of pics that came out in the local version (Oct 2011 issue) of FHM magazine: a deathmatch series between different Philippine creatures! I stumbled upon this stuff from Trese's website -- it's awesome.
Tikbalang vs. Sigbin!