I did a long trip surfing to Fuerte a couple of years ago, the place is great for any kind of water activity, especially windsurfing.
In Corralejo, up North, you have access to the infamous "North Track" a dirt road that leads you along some of the finest breaks in Europe, and it is also the main tourist stop for the Island. In this area there is Flag Beach who do rentals (Fanatic), the main bay with some mickey mouse operation, or you could take a trip out to Los Lobos on a boat to watch the locals tear apart a point break. Flag Beach do kitesurf lessons if the wind is not so good, but make sure you ask for Gunnar. If there is no wind here, call the guys at Rene Egli to see if the wind is any better there. The boys running the centre at Flag Beach will tell you there is no wind there to make you stay, but in reality you could be overpowered on a 4.7 down south. The water in Flag Beach is quite flat with a bit of a wave out back, but can get pretty meaty. Also worth a visit is Corkys and Oink in town, though go later as it can get a bit messy if you go out too early... Surfboards can also be rented from the many surf shops.
The world famous Rene Egli Centre
http://www.rene-egli.com/ (Sotavento) do Neil Pryde and JP, although they are rather expensive and German biased. They also do kitesurfing. Problem here is the wind is usually offshore and usually pretty strong and rescue cover was non-existant!
I went early season and the wind was a little unreliable, high season its pretty much guaranteed, and then this time of year it starts to get a little unreliable again.
All in all, well recommended.