It depends on what kind of quality you are after.
If you want a cheap job, with prop shutter effects and plenty of distortion
then any of the £100-£300 cameras commonly sold in pilot shops these days (GoPro etc etc) will do it... a bit of duct tape or a suction cup, etc
If you want a classy job then you need a reasonable quality camera, and a proper way of mounting it which does not transmit vibration.
You also need a clean scratch-free part of the window.
Plus avoidance of reflection from objects in the cockpit; may need dark clothing, etc.
I can't think of anything you could rig up for tomorrow, but
here are some pics of a mount I have constructed and used very successfully with a forward-shooting camcorder. The four little anti-vib mounts came from
this company, at about £15 each.
This method has the advantage of not requiring pilot interaction during the flight, but you need sufficient in-camera storage for the required flight duration or whatever.
Otherwise, with autopilot, or a co-pilot, and a camera with good motion stabilisation, you can get good enough handheld results e.g.
this. No antivib mounts are needed.