Pagsanjan falls (approx. 2 hours from Manila) -- river rapids boat ride and waterfall
http://www.intas-travel.com/incentives/discover_fil_soul.html

The neighboring areas are noted for woodcarving and other handicrafts, so you could go look at those in the afternoon if you're interested, or we could return to Manila or move on to the next destination.

Subic (about 3 hours from Manila)
http://www.mangossubic.com/Things_to_do.htm

Also within Subic is a virgin forest where one can go on a trek, visit a tribal village, and take a jungle survival course. Subic Bay is a rich hunting ground for both professional and Sunday anglers alike.

There is lots to do in Subic ... mostly water sports. The beach is rather mediocre compared to other Philippine beaches but there are all sorts of activities, so it's a popular resort spot. They also offer horseback riding, go karting, etc. It used to be a US Naval base until the lease expired several years ago.

There is also an ultralight flying club about an hour from Subic (closer to Manila), if you want to try flying in a small plane (I think it's about P800 for a half hour flight in a 2-seater)

Tagaytay and Taal Volcano (about an hour's drive from Manila)
http://www.flyphilippines.com/info/tagaytay-philippines.html

Taal is supposed to be the smallest active volcano in the world (the last time it erupted was 1976). It's a popular weekend destination because the view from the ridge is great, and the temperature is relatively cooler than in Manila. The restaurants along the ridge serve very good Filipino food. This is where we took Prabs and Monique when they were both here.

There is also a small yacht club on the lake that offers hobiecat sailing -- John and I took sailing lessons there last year.

Villa Escudero (about 2.5 hours drive from Manila)
http://www.villaescudero.com/

This resort simulates a Philippine coconut plantation. They offer rides on a carabao (water-buffalo) drawn cart, a Filipino lunch at a waterfall (basically, you take off your shoes and the river water is running over your feet while you're eating. the food is served on plates lined with banana leaves), and a cultural show with several Filipino dances and musical numbers.

Hidden Valley -- hot springs, nature walks, rainforest. If you want to go swimming, this is a nice place. The Filipino food they serve here is also very good.
http://asiatravel.com/philippines/other/hiddenvalley/

Intramuros -- the old Spanish walled city (inside Manila -- half day or less total time) http://www.lakbay.net.ph/tours/metromanila/intramuros.html

This is the original city of Manila, and still contains Spanish cathedrals and Fort Santiago. Casa Manila is a museum of Spanish colonial furniture, costumes, etc set in a restored Spanish house. Good if you're a history or culture buff. It's also close to Malate (a top nightlife destination for dinner).

Corregidor (maybe an hour by boat from Manila bay) http://www.marsman-tours.com.ph/dt09.htm

For military history buffs. This one is a whole day. There is a sound-and-light show about World War II and the American defense against the Japanese.

Corregidor is a tiny tadpole-shaped island lying across the entrance of Manila Bay. Also known as "The Rock," it was the focus of a protracted battle between Filipino-American and Japanese forces during the Second World War. The shell of the Mile Long Barracks still stands. Within the Malinta Tunnel, a light-and-sound show is staged for day tourists. It can be reached by de-luxe cruisers from the CCP Complex jetty in Roxas Boulevard.