I am sure that this list does not include all of the activities available but it is a good start…

Tours, Sailing, Zipline, Hiking and More

Baja Outback: bajaoutback.com
Ecotours: caboecotours.com
Cabo San Lucas Tours: cabosanlucastours.net
Cabo Adventures: cabo-adventures.com
Cabo Canopy/Zip Lines: wildcanyon.com.mx
Cabo Expeditions: caboexpeditions.com.mx
Pez Gato: pezgato.com
 

Snorkeling and Scuba Diving

Dive Cabo San Lucas: DiveCaboSanLucas.com
Andromeda Divers: scubadivecabo.com
  Also, many of the companies in the Tours section offer snorkeling and diving.
 

Charter Deep Sea Fishing

The pastime that first put Los Cabos on the tourist map is sport fishing. The waters teem with more then 850 species of fish, including several varieties of marlin as well as swordfish, dorado, tuna, wahoo, snapper, cabrilla and grouper.

Winner 7: winner7sportfishing.com
Dave/Kathy (Winner 7) are good friends of mine and will knock themselves out for you!
Cabo Magic: cabomagic.com
Red Rum Sportfishing: redrumcabo.com
Picante Sportfishing: picantesportfishing.com
Slippery Lizard: slipperylizardsportfishing.com
Cabo Sportfishing Fleet: cabosportfishingfleet.com
Cabo Fishing: cabo-fishing.net