It's not as reliable as Viagra but for some men it does help and it can't hurt.(No, I personally have nothing on which to try it, but I am a sex therapist.) Michael Castleman has written on ED therapies elsewhere on TBD.

While I don't have ED, I have used a mixture of L-Arginine and an herb called Muira Puama Root to strengthen my erection. and it seemed to work well. Harder is better ya know.

It is my understanding that the L-Arginine works to keep the blood vessels less constricted, increasing blood flow to the genitals. The herb apparently creates an effect in the bloodstream similar to capsaicin ( the HOT in hot peppers ), stimulating tissues the blood courses through.