Linear regulators actually make for good constant current sources because of fairly high accuracy between the output voltage and ground.

All you need is a resistor between output and ground to limit your current.

I_out = V_out / R_out

I will refer you to this Maxim application note for a more thorough explanation.

http://www.maximintegrated.com/app-notes/index.mvp/id/4404

Linear regulators actually make for good constant current sources because of fairly high accuracy between the output voltage and ground.

All you need is a resistor between output and ground to limit your current.

$$I_{out} = \frac{V_{out}}{R_{out}}$$

I will refer you to this Maxim application note for a more thorough explanation.