We're still working on this but here are some links to some projects and plans for the future of transit in Washington:
DC's Transit Future (archive.org version): http://web.archive.org/web/20070811223553/http://www.dctransitfuture.com
Purple Line: http://www.bi-countytransitway.com
WMATA Planning & Development: http://www.wmata.com/about/expansion/expansion.cfm
Corridor Cities Transitway: http://www.cctnow.org
Dulles Rail: http://www.dullesmetro.com
West Ox Division: http://www.fairfaxcounty.gov/connector/west_ox.htm
Subsequent takeover of Metrobus 2W, 12 & 20: http://www.fairfaxcounty.gov/connector/pdf/12s_20s_approved_plan.pdf
Columbia Pike Streetcar: http://www.piketransit.com
K St Busway: http://www.nc3d.com/projects/k-street-busway-2.html | http://www.wmata.com/about/expansion/kst_busway.PDF
Discuss the future in the DCATZ Forums: http://www.dctransit.info/forums/index.php#3