Today, in addition to the Pedersen case being brought by GLAD, the ACLU LGBT Rights Project will file a complaint challenging the constitutionality of DoMA in federal court in New York City. New York, like Connecticut, is in the Second Circuit, so both cases will eventually reach the same Court of Appeals. Also like the GLAD cases, the legal claims are founded in the Equal Protection Clause.
What is new and different about Windsor v. United States is that it is the first case to challenge the estate tax, and it seeks relief on behalf of a person who does not live in a state that performs same-sex marriages. Plaintiff Edith Windsor married her now deceased partner Thea Spyer in Canada in 2007 and the two lived in New York, which recognized their marriage. After Spyer died in 2009, Windsor had to pay a huge amount in estate tax – $350,000 – which she would not have had to pay if the federal government had recognized the marriage, as New York state does. She is now seeking to recover the payment, which is the largest amount of money at stake in any of the DoMA challenges.
The state attorney generals in Maryland and Rhode Island have issued formal opinions (AGOs) declaring that those states would, like New York, recognize same-sex marriages validly performed elsewhere, even though the state doesn't treat gay marriages performed within its borders as legal. So far as I know, no litigation has been based on or tested the Maryland and RI AGOs.
A film about the Windsor-Spyer relationship – "Edie and Thea: A Very Long Engagement" – won the prize for best documentary at the 2009 Hamburg Lesbian and Gay Film Festival. The NY Times featured their marriage in its wedding announcements.