Cancún Waterski and Wakeboard (Marina Manglar, Blvd. Kukulcán Km. 19.8, cell. tel. 998/874-4816, www.waterskicancun.com [1], by appointment only) has three slalom courses and a number of ski sites at the southern end of Laguna Nichupté. Free skiing and wakeboarding cost US$200 per hour, while the slalom courses are US$50 for 15 minutes. Cash only.
The Asociación de Surf de Quintana Roo (Quintana Roo Surf Association, Blvd. Kukulcán Km. 13, cell. tel. 998/118-2466, www.surfcancunmex.com [2]) offers surf classes and rentals. It also hosts occasional surf competitions. The group has a kiosk (8 a.m.–6 p.m. daily) on Playa Delfines [3], which is generally the best surf beach.
Links:
[1] http://www.waterskicancun.com
[2] http://www.surfcancunmex.com
[3] http://www.moon.com/destinations/cancun-the-yucatan/cancun-cozumel-and-the-riviera-maya/cancun/sights/zona-hotelera-beaches