From Phil Endecott:
With Topo Maps view USGS 1:24,000 topographical maps on your iPhone or iPod touch. It features downloadable maps, locate the maps you need on the satellite view, search by name for maps and about 8,000 national and state parks, forests, and wildlife areas, see coordinates in NAD27 or WGS84 degrees, degrees minutes and seconds, UTM, or MGRS formats, and measure distances and bearing.
What's new in this version:
Version 1.7 added waypoints to maps and import and export waypoint files, search now includes 1.5 million features, new GPS symbol that keeps map centered on your location, compute what should be visible from any viewpoint, color maps according to height, and measure bearings in mils.