Here's a great story of archaeological and genealogical detective work from the Washington Post. Smithsonian researchers have successfully identified a boy found buried in an iron coffin in Washington, D.C. He is William Taylor White, who died in 1852.
The identification was made after museum researchers, led by Deborah Hull-Walski and Randal Scott, figured out that the youth might be White, constructed a 788-person family tree -- a diagram that stretched the length of a wall -- and tracked down a descendant in Lancaster, Pa.
The descendant, Linda Dwyer, 64, a night clerk in a convenience store, agreed to provide a sample of her DNA, obtained via a mouth swab, and when that was compared with DNA taken from the boy's left shinbone, it matched.
She said elated Smithsonian researchers called her with the news, saying: "'It's you! It's you!'" [Link]