Is there a way to turn off the sleep mode in the 430EZ flash? It seems that after it is on and not being fired after a minute or so, it goes into sleep mode.

It's Canon's "Save-Energy" function, and there's no way to disable it unfortunately..

One option is to jam the light button to keep it awake:

http://www.flickr.com/groups/diyphotography/discuss/72157623005554633/