From the Washington Post:
"The average rental vacancy rate in the Washington area in the fourth quarter of 2007 climbed to 3.7 percent from 2.9 percent a year before. Rents increased 1.8 percent in the past year, the smallest rise in five years.
. . .
Management companies said more prospective tenants are shopping around in the growing rental market and asking more about concessions or enticements such as free rent or a flat-screen television".