Depends on what style of flying you are doing now, and/or you are planning to do later on. 

Swash Servos - you need 3

The idea here is to get higher speed and higher torque ones for the swash, since this is where most of the action is going to happen !

If you want to just fly around with sport flying, even the simple Futaba 3003s (QR 50 each) will do !  If you crash, most likely some of the plastic servo gears on these would get stripped. Of course, this is not preferred at all, unless you are really tight on dough 

If you are investing for the long term, and/or into agressive 3D (now or later), then get some good metal gear digital servos.  I have had great success with the Futaba 9451s, although they are built for RC cars.  The new version of these are the 9452s.  There are also the new brushless servos from Futaba, like the BLS431s.  There are also good metal gear servos from Hitec, which are frequenty used around here.  I know our local master Joe uses them a lot. 

The top of the line currently seem to be the JR8717s, which can run straight off a 7.4 volt 2-cell lipo.

Throttle servo - you need 1

Unlike the swash servos, the throttle servo need not be high speed digital ones, pretty much any ordinary non-digital servo (Futaba S3001 or S3003) should work fine.  If you want to go digital, the Futaba S3151 seems to be a popular choice (for about US$30).

Tail servo - you need 1

For the tail, speed is the most important factor.  So typical servos like the Futaba 9256 used with the GY611 gyro is a good choice.  Or the LogicTech 6100T servo that comes the LogocTech 6100G gyro is a even more sensible choice, since it performs on par with the Futaba 611, but costs about 30% lower.