This is a brochure from the Montgomery County Register of Wills Office that explains why Revocable Trusts are not everything they are advertised to be:
The D.C. Superior Court Probate Division has some good information about probate: https://www.dccourts.gov/internet/superior/org_probate/main.jsf
A helpful website for Maryland residents with probate and estate information: https://www.peoples-law.org
DC estate tax is currently imposed on estates over $1,000,000.00, but this could be changing in the near future.
The federal estate tax exemption is currently over $5,000,000.00 (as of 2014): https://en.wikipedia.org/wiki/Estate_tax_in_the_United_States
Maryland recently revised their estate tax to eventually be consistent with the federal exemption level.