My opinion is that you cannot go wrong with a classic suit for interviews. Nordstroms, or any dept store would be fine. Ann Taylor, or Ann Taylor Loft can be good too.
My agency is business casual, but we always expect people to come to interviews in suits.
And if a suit is a bit overdressed, that doesn't bother me. For interviews, I would err on the side of being overdressed than too casual. Also, if you're interviewing for positions in which you'd have client exposure or in some other way represent the company externally, it's good to show that you can get dressed up.
If you still have contacts/friends who are at the kind of companies you're aiming for, they might have the best answers for your specific situation, though.