Pony Expeditions (Jr. Sucre 1266, tel. 043/39-1642, www.ponyexpeditions.com [1]) was founded in 1993 by Peruvian couple Aidß and Alberto Cafferata, and is the most solid adventure outfit in Caraz. It has top-rate equipment and offers a range of climbing, trekking, mountain biking, and fishing trips. Treks offered include the famous Santa Cruz loop (four days/three nights, starting from US$200 pp), Alpamayo (12 days/11 nights, starting from US$600 pp), bike rentals to Cañó del Pato (US$18 pp), and guided climbs on nearly all of the technical peaks around Laguna Parón. English and French are spoken and there is a good gear shop where you can rent camping equipment and buy camping gas cartridges and very good maps.
Another good agency is Summit Peru (tel. 043/39-1958, www.summitperu.com [2]). Because the company is primarily Web-based, it is a good idea to get in touch with Carlos Tinoco and Haren Montes, its operators, before you arrive in Caraz [3]. Carlos and Haren organize a variety of trips and provide reliable equipment.
Links:
[1] http://www.ponyexpeditions.com
[2] http://www.summitperu.com
[3] http://www.moon.com/destinations/peru/huaraz-and-the-cordillera-blanca/callejon-de-huaylas/caraz