Restaurants
While not mandatory, is desirable. Locals will tell you 10% (or less) is standard and tourists will normally tip more.

Spas
15-20% of the service is standard at most spas.

Taxis 
Taxi drivers do not expect to be tipped unless they perform some extra service such as carrying your bags or luggage to your hotel entrance, etc.  But almost everybody leaves them some. Usually the coins change. 


Ushers in movie theaters

One peso for showing you to your assigned seat. At he actual inflation rates, 50 cents is nothing compared to the ticket price.

Hotels

A minimum of one peso per baggage for taking luggage to your room. But with that minimum you are not gaining any further service. Better make the minimum a 2 pesos bill.

Bus 

If you take a long distance bus and you have luggage to put in the hold, remember to tip the baggage handler a peso per bag when your bags are put in or taken out of the hold.