I received this reminder at work from DHS today.
The 2005 law (yes, this was passed by Congress in 2005) will finally be implemented tomorrow, Wednesday May 7. You will need a federally-authorized form of identification to air travel domestically and enter federal properties such as courthouses, passport agencies, etc. A standard issued state drivers license is no longer acceptable. If you have an enhanced DL or a passport, those are accepted, amongst others.
Homeland Security has stated that for now, if you show up for a domestic flight without a REAL ID, you will still be allowed on a flight, but you will be subject to additional questioning and enter through a more rigorous line of security. So expect that to take longer.
REAL IDs are available at most state DMV centers.