All foreign visitors must have a passport valid for at least six months beyond the intended period of stay and return or onward tickets and documents necessary for further travel. 

As of August, 2013, no visas are necessary for a stay up to 30 days for residents of 151 countries. This is up from the previous allowance of 21 days If you intend to stay longer than 21 days, it is often cheaper to apply before you travel to the Philippine Embassy in your country. For some countries such as China, visas are required.

You can visit the Philippines Immigration Website for information regarding which nations quality for the 30 day visa waiver