You can now easily extent your stay in the Philippines for up to 16 month without ever having a Visa for the Philippines and without ever leaving the country.
Most foreigners enter the Philippines without any Visa and they will get a stamp in their passports which is good for 30 (new!) days.
If someone wants to extent their stay, you would have to go the nearest Immigration Office and get your first extension, good for another 21 days.
Now you are already 59 days in the Philippines and your regular extension series starts by showing up at the Immigration Office every 2 month, just maybe a couple of days before your stamp expires.
The ACR Card
If you make the next extension at 59 days, the immigration office will also issue an ACR Card (50 US$+500 Peso) for you, which makes this extension more expensive than the other ones.
If you have to go to the Immigration Office, make sure to wear long pants, a nice shirt and shoes. Otherwise you might not be serviced, some Immigration offices (Cebu) might not even let you in.
Cost of Visa Extension
Every Extension has different fees and will cost between about 3000 Peso and 5600 Peso. The expensive one is when they will issue an iACR Card. For all extensions you can do within one year you'll end up with about 26,000 Peso.
Since August 2007 you may extent your Visa for up to 16 month in total. After 16 month however you should finally make a Visa Run or try to get another extension for up to 24 month from the "Chef of the Immigration Bureau for Regulations". Since this might become too complicated, it might be easier to make a Visa Run or to try to get a permanent residence.