Has anyone driven a small 5Volt relay directly from an Arduino output? Or does the turn off spike kill the pin?

It's unlikely to supply enough current to energise the coil. But if it did, you must include a flyback diode as shown in (a) in khalil's diagram. You don't need 2 diodes like in (b).

Don't wire the relay to a 12V supply like in Kahlil's diagrams. Arduino doesn't use open collector drivers so you'd damage the chip. Instead drive the relay directly from the Arduino output.

What "pin"? Sounds  more like a solenoid.

If you refer to Back EMF fr relay, it can damage, Especially at hi current/many turns of wire. Faraday's law and ampere/turns.

A small reed wont need any protection. Maybe a 1N4001 across the coil, the anode  (striped end) to negative,  cathode to +. I do on every relay or motor I add to my car,  just in case.  Reduces noise in radio, too. 

thanks all but got it working fine direct drive (with flyback diode) from 5 Volt rail. Used a reed relay - pulls about 10mA.

Hi this is when you need a transistor to drive the relay even a bc109 would at least drive a small relay however you will need a diode connected in reverse direction so it protects the transistor across the relay's coil. otherwise when the transistor switches off the back e.m. f. will destroy the transistor with a reverse high voltage spike.

if the output cannot provide enough current for the relay, we may use a driver ( usually a common emitter transistor )..

yes ... we should use a damper diode to clip the spike ..D1 in fig. (a)