Strongest / most aggressive 1. d4 openings I'm curious to know what are some of the 1. d4 openings (Queen's Pawn), especially if they are highly agressive and/or are regularly used at higher GM level of play.

I really want to learn all I can and focus on d4 openings everytime I get to play white. I currently play the London System Opening.

All recomendations are welcome.
I feel that the most ambitious, principled and aggressive 1.d4 repertoire is the one given by John Cox in his book "Starting Out: 1.d4!". Of course these are the most ambitious lines for white in chess so they have also got extreme amounts of published theory and as they lead to very sharp positions, not knowing the theory may lead to quick losses for white.

The main criticism of the book was that a collection of lines fit for top players may not be suitable for the audience of "Starting Out" books, but you don't ask for easy openings :-). Ironically even the world top has now moved away somewhat from these lines because the theory had been worked out so far, they go for slightly more restrained lines with g3 or so more of the time these days.

It is based on 1.d4 Nf6 2.c4 and 1.d4 d5 2.c4.

The following list of the lines it offers is from Watson's review of the book (http://theweekinchess.com/john-watson-reviews/the-end-of-openings-part-1), as I don't have the book with me right now:


  Cox's book suggests a complete repertoire for White beginning with 1
  d4. Here are a few of the main systems that he recommends:
  
  (a) versus the King's Indian: the main line 4 e4/5 Nf3/6 Be2/7 0-0 and 9 b4, the Bayonet Variation, , one of the most theoretical lines possible, with
  Black systems to cope with on every move that leads up to that move;
  
  (b) versus the Grünfeld: the main line of the 7 Nf3/8 Rb1 system, that
  is, the one that Edward Dearing recently wrote a densely-packed
  205-page book about;
  
  (c) versus the Nimzo-Indian: 4 Qc2 and pretty
  much every main-line line that follows this most investigated of
  modern lines;
  
  (d) versus the Benoni: the Modern Main Line with h3 and
  Bd3, again the most-analysed current variation;
  
  (e) versus the Benko
  Gambit: g3 and Bg2 with the contemporary main variation 10 Rb1;
  
  (f) versus the Queen's Gambit Declined: the main line Exchange Variation
  with the sharp Nge2;
  
  (g) versus the Tarrasch Defence, the main line: 6
  g3/9 Bg5, also ridden with traps and tricks to remember;
  
  (h) versus
  the Slav Defence: the main line with 6 Ne5, the most theoretical and
  complicated Slav line ;
  
  (i) versus the Semi-Slav: the main line
  Botvinnik Attack, one of the most-analysed variations in all of chess
  history.