I bought an iphone not that long ago, and it seems to me that the one application that is begging to be written is a GeoCaching website specifically optimized for iphones. I know the iphone doesn't have GPS, but alot of GPS don't have internet connections or data/memory for showing the rest of the geocache data. It would save me from having to tote around my Axim which has lately stopped working so well. :(
It seems lately that this topic is getting alot more attention. Somehow this blog post is #1 on google for the term [iphone geocaching] and I'm seeing alot of traffic for this term. There are still no good solutions as best as I can tell. I'm pretty interested in watching this space though, so I've created a knol to follow all of the current options. I'll keep the knol updated with any changes, so if you are interested bookmark or visit iPhone Geocaching on Knol.