The taxis in Gran Canaria are really good. We were lucky as when we wanted a taxi from our accomodation, our barman called us one! It came really quickly and the driver was great. The taxis are really cheap as well, if you are just looking to go a short distance. For example, we went from Maspalomas to Playa Del Inglis by taxi and it cost us about 3 euros. There are taxi ranks all over the place, and they are really easy to deal with.
A word of warning though, if you are looking to go a bit further afield, a taxi will really hike up the price as soon as you go onto the motorway!
The cheapest way to go around the island is by "guaguas" (buses). The service is quite good, very cheap and on time!
Try to learn a bit of Spanish, the drivers could be very rude...
Check their websites you can print out your own timetables, it will save you from waiting for ages (not all buses are frequent....).
No matter what any one says, in a derogatory manner about the buses, IGNORE THEM, the service to and from the airport is fantastic. The bus is always on time...runs from early morning to late evening and costs €3.20...as against €35+, before the tip, were one to travel by taxi! Route 66.....25 mins past the hour from Iguazu 3(a central example) but pick-up points over a large area. LESS convenient coming from the airport as many will be 'in a hurry'...still, if you can wait until 20 past the hour, the a bus every hour from just to the right of the taxi pick-up point at the airport. NEVER consider a taxi to Los Palmitos Park... a waste of money and were you never travekl sick before, you might well be after THAT! Take the bus.
You will probably be told by your travel rep (if you do the package holiday thing) that the bus services around the coast of Gran Canaria are great!! They quite possibly are if you can speak and read fluent spanish and understand the roundabouts on top of roundabouts with a bus stop in the middle!!
I found the buses in Maspalomas rather confusing - especially where we had to try to get one (outside Holiday World). The Canarians definately seem to like their roundabouts - we had about 4 roundabouts joining with about 3 bus stops dotted around (what appeared to be) randomly.
The first day we tried to catch a bus, (we wanted to go to Peurto Rico) we started at one bus stop and waited for about 30 minutes without a single bus stopping for us. We then thought 'maybe we are at the wrong stop' - so we proceeded to another. We then waiting here for another 30 minutes and all the busses were going to the wrong place - so we gave up and went to CC Faro 2 for lunch. We then came back and went to the third stop for another try. This time a bus stopped and the bus driver proceeded to tell us that the first stop we had tried was actually the correct one!!! Aaaarrgghh!!
We did actually eventually get there, and once we understood the system, it was a little easier!!