These are the two places I know of where you can donate money from outside Costa Rica: Western Union and Tico Bingo online. The money ends up at the Cruz Roja [cruise ROW-ha].
Cruz Roja is literally Cross Red, or Red Cross. They are the relief
program here. Donating to the Red Cross in the states will not, as far
as I can tell, trickle down to Costa Rica. The Cruz Roja is critical
here, they rescue people all the time from flooding and landslides. I
don't think they have enough money to be corrupt… but who knows.
Western Union
You can make donations for earthquake victims from outside Costa Rica via Western Union. You are donating to the Cruz Roja (literally Red Cross, er, Cross Red). Tell Western Union it's for "Cruz Roja, EARTHQUAKERELIEF CR". It is a free transaction. You need an office where there are people, not just a machine.
Tico Bingo
You can donate to the Cruz Roja's Tico Bingo online using visa or mastercard. Tico Bingo is how the Cruz Roja raises money. Often you'll see the Red Cross guys and gals in the street in front of your local Cruz Roja office selling bingo cards for un rojo [oon ROW-hoe, one red which is a 1000 colon bill, $2]. That's the gringo price… but I'm happy to pay it!