Most shopping centers and many public places including some parks have free wi-fi access points, although speeds are sometimes not the best. Almost all cafes and most restaurants offer wi-fi for clients. Generally all hotels and hostels have good wi-fi available, although it does not always reach into the rooms, so check before booking if this is important.
There are plenty of internet cafes in El Poblado and the center. Most charge around COP$2000 per hour. Try the Internet Center.