The torque of the engine causes the plane to yaw left. To counteract this, you can do a few things:

1. Input (small amounts of) right rudder
2. Apply the throttle more gradually on takeoff.
3. build a couple of degrees of right-thrust in to the engine mount.

The basic premise is that with the revolving propellor generating thrust, there is a counter-force (newtons laws of force - every action has an equal and opposite reaction), and that counterforce of the revolving prop is yawing the plane. This is very normal, and the common consensus is "learn to deal with it".

I'll edit this post to add a few links.

gus

P.S. Here's a good link [link=http://www.rcuniverse.com/forum/m_290989/mpage_1/key_torque%252Cthrust%252Cright/anchor/tm.htm#290993]Aerodynamic discussion of right thrust[/link]