GPS app for the iPhone?

Is there a good GPS app for the iPhone I can download? My brother and I are going out tomorrow and want to take the tandem (netting is way easier from the tandem), but it has no electronics. If I can bring my iPhone with a GPS system on it, that would be a good fix. Any ideas?
Thanks!
Andrew

Check out the Navionics app for the iphone, there was a thread just posted about it on here.