Can anyone suggest a response to 1. d4 that would create a more open and tactical game than my usual 1...d5?  Any help would be most appreciated!

Nf6

Try the Benko Gambit, Benoni Gambit, or Nimzo-Indian defence. Grunfield maybe.

nardis- you want to create an open, imbalanced, tactical game.. so the modern benoni or the grunfeld would be sharp choices. budapest gambit is another fun try

Oh yea, forgot all about the Budepest. Love that opening.

By the way, you can check out an article (or 2, forgot) about the Nimzo by the two GMs Arun and Magesh on chess.com if you search for it :) It should be fairly recent, page 1 or page 2 of the articles.

We have a search function people...

http://www.chess.com/forum/search.html?keyword=against+d4

Funny - it seems to me that Lasker, Rubenstein, Capablanca, and Alekhine all had wonderful success with Black with 1 ... d5.  Anand, Aronian, and Topalov still do.

There are lots of more tactical choices for Black in the QGD - the Slav, Meran Complex, Ragozin Variation, Tarrasch Defense, to name a few.  You don't have to go to some obscure opening to find complications.  Most of them are obscure for good reasons.

Most of the people you will "catch" with a weird opening line are people you would beat anyway.  The "main lines" are the main lines because they have passed the practical tests at high levels.  Play the good stuff - you can get a playable position well into the middlegame from many of the "normal" defenses, and it is unrealistic to expect much more from your Black repertoire.

Queens Indian?

Marshall defence.

The Albin Counter-Gambit is usually tactical and interesting:

Check out the stats in your database, Black does surprisingly well.