Hoisted from the comments from my post on creating ESRI ArcGrid DEM files for use with Terrain Bender, two more options for converting other DEM formats to ESRI ArcGrid, plus many other formats as well.
LandSerf: A multi-platform (Windows, Mac and LInux) terrain visualization and analysis program, LandSerf can also import/export DEMs in a number of formats (.bil, .flt, .grd, .asc, .dem, .bin, .hgt, .ter, .bt); VRML (.wrl) is an additional export format.
VTBuilder: Windows only, VTBuilder lets you import/merge/resample DEM data in any GDAL-supported elevation format (and several additional ones like MicroDEM DEM files), and export the data in the following formats:
- ArcInfo ASCII Grid (*.asc)
- TerraGen (*.ter)
- MSI Planet
- VRML ElevationGrid (*.wrl)
- RAW/INF for MSFS
- ChunkLOD (.chu)
- VTP (*.bt)
VTBuilder was primarily designed for use in putting together data for the Virtual Terrain Project, an open-source 3D landscape visualization program. The VTP site contains a wealth of links to software, data, and general information about terrain visualization, and is well worth a look.