Greg:
I know you asked for specific information on providers, but I can't help myself...
Costa Rica is absolutely beautiful. Spanish and English are both considered "national languages" and nearly everyone speaks English, so you should have no problem communicating even if you're not bilingual in Spanish.
I'm assuming you plan on hitting the Caribbean side of Costa Rica, and there are some great dive spots out there. Some of the best coral reefs in Costa Rica are in Limon, protected inside Parque Nacional Cahuita. There are plenty of hotels and resorts in Limon that offer snorkel or dive packages, but you can also find a number of independent dive operators that offer day trips to snorkel or dive.
Another great experience in Costa Rica is a canopy tour - it's an amazing, thrilling way to get a glimpse of Costa Rica's diverse ecosystem from a different point of view. And a trip to Tortuguero National Park will reveal one of the largest sea turtle nesting sites on the continent.
If you're interested in surfing and you have the opportunity, head to the Pacific side, northern part of Costa Rica to Tamarindo. It's a surfer's paradise and is an absolutely charming little town. The beaches near Guanacaste and Playa de Conchal are also nice for relaxing, and the shopping in Guanacaste is pretty fun.
Whatever you do, be sure to sample the local cuisine via street vendors and small shops, talk to the residents and find the good nightlife.
As for the ladies...
Costa Rica Chicas
The Real Costa Rica
Costa Rica Link