The Halcyon-class cruiser (specifically the Pillar of Autumn), based on the model from Halo: Reach. Intended for printing at smaller scales (10.1cm/4 1/4 in.), but I have a version made to print at larger scales that I've been meaning to upload.
NOTE: It's oriented vertically so that it needs minimal scaffolding/support, but this version had trouble with the thrusters when I printed it, where they would be filled with sprue and it was impossible to remove any of it without damaging the engine baffles. I also had some minor issues with the rear outer guard(?) not connecting completely to the sides, but I think I fixed that with this version. If you print this one and it fails, check out the other one I'll upload which should fix any problems with this one. (If it's not uploaded by the time you find this, post a comment and remind me, I've been a bit busy lately)
Also, the second image is from the updated print and not this file (and also LARGER than this - remember the scale I specified before), but the end result is fundamentally the same obviously.