There was a great story in the Boulder Daily Camera about the SmartTrails app. The developers are seeking a grant to help them get this worthwhile project off the ground. If you'd like to help them out and put them over the top, you can vote for their grant idea on the GOOD Boulder Fund website. It's easy to vote, doesn't cost you anything and helps support a good trail cause.
So far, the only problem I see w/ this app is that it's not quite available for iphone yet; but according to BMA rep. Andria, they are on top of it. In fact, they "have an iOS developer working in parallel..." What I think that means to us non-techie folks is that they are soon going to have an [iphone] app for that.
If you want more information about the app, you can drop an email to email@example.com.
In the meantime, I'm curious what apps, GPS, or other trail-navigation devices you guys are using out there. Leave a comment below.