I agree with Damien on the surgery, and the injections are a temporary fix. Your focus should be on removing the source of irritation, because even when removed, more neuromas can form. You already have at least three.

The internet chatter out there suggests if you are using cleats, to move them in back of the ball of the foot. Don't use toe clips at all, because they will bunch the toes in any soft shoe, and there is a riding sandal by Lake that will give your toes some room, if you are careful to protect them while riding.

Someone else suggested platform pedals, but shoes even when sized correctly may bunch depending on how you drive the pedals and how the shoe is fastened. Many bike shoes have fastening systems that may not prevent the toes from bunching. One problem is pressure on the forefoot while trying to grip a surface with the forefoot. The muscles in your foot can cause the metatarsals to squeeze together, pressuring the perineural fibrosis (aka "neuroma"), and this effect has to be eliminated by secure footing.

I found just today that I could irritate the nerves in my foot by working the pedals on a piece of gym equipment. It happened when I was trying to grip the pedal with my foot while placing pressure directly on the balls of the foot (metatarsal heads). Ordinarily, this pain does not bother me when running after I tape my toes properly to separate them.

To summarize, it appears that a secure cleating system + no pinching, jamming, or sliding in the toe box = no pressure on the neuroma. Even though you are not running, other riders suggest your feet will still swell, and this must be accounted for by sizing up your shoe and securing it properly, so the foot does not pinch by outgrowing the shoe or sliding in it, as Damien cautioned.

Further reading:

http://forum.cycleoregon.com/viewtopic.php?f=1&t=464&start=15

http://community.active.com/thread/35089/mortons-neuroma-argh