The U.S. government has released its 2005 Federal Radionavigation Plan [PDF, 74 pages]. Here is what they are proposing for each type of aviation-related navigation aid:
- GPS
- Will be the primary federally-provided radionavigation system for the foreseeable future. Will continue to work on augmentation, both through initiatives like WAAS, and by providing two new civilian signals, L2C and L5, to support special operations (like lifesaving).
- Loran-C
- Will continue to operate until the end of 2006, while evaluating long-term need. Promises at least six months notice if the system is going to be shut down.
- VOR
- Will phase down the VOR system (enroute and approach) beginning in 2010, based on anticipated decline in usage, but will still a “minimum operational network” (MON) of VORs as a backup to GPS.
- DME
- Will maintain the existing DME service to support RNAV systems. Plan to install more low-power DMEs to support ILS precision approaches.
- TACAN
- Will keep the air-based TACAN system until all military aircraft are properly integrated with GPS for national and international controlled airspace (not sure if this applies to all NATO aircraft, or just the U.S.). Sea-based TACAN will continue indefinitely.
- ILS
- Will reduce the role of Cat I (regular, 200 ft DH) ILS approaches as GPS precision approaches come in, beginning in 2015. ILS will still be available at major terminals.
- MLS
- Not installing any more systems. Will phase out existing installations beginning in 2010.
- NDB
- Most NDBs will be phased out, except for those that serve International Gateways, and those in Alaska (for LF airways, similar to the airways in northern Canada). Some may be kept for missed-approach procedures. Phase-down began in 2005.
- Marker Beacons
- Will be phased down, replaced (in many cases) with published DME distances, navigation waypoints, etc.
So, I’ll be good for IFR in my Warrior for a few more years without an IFR-certified GPS, but I’d better start a savings fund if I want to do precision approaches after 2015. It looks like the DME receiver in my panel will be useful for a while longer, though.
Land and Hold Short 
How are you going to have a non GPS approach at an alternate airport if the FAA decommissions the ILS and VOR system? Is it suddenly going to get more reliable? … GPS RAIM UNAVBL.
–paul
Note that they’re merely thinning out the VOR and ILS networks, not eliminating them — you’ll have a smaller choice of alternates available, but larger airports (however that’s defined) will still have ILS, and there will still be a skeleton network of VORs.
Maybe they’re also hoping that the Galileo network will be available as a satnav alternative to GPS by then.