Not a lot of choices in .45.
The thompson is heavy, but a classy choice.
Marlin's Camp 45 uses 1911 mags and is popular for that reason. Needs an immediate upgrade of recoil spring to 21 pounds from Wolf. Marlin was dumb in the initial release with the weeny spring they put in there.
Hi-Point keeps threatening to put out a .45 carbine. They still haven't yet.
There's the HK. But you suck, and they hate you.
Ruger's PC carbine is only in 9 or 40.
Beretta's carbine is only in 9 or 40.
MechTech CCU's are available for existing 1911 or Glock frames to get to .45acp. $300 and it isn't a standalone firearm, though. Kinda annoying, IMO.
Or, you have AR uppers in .45acp. I believe you have to use a Cavalry Arms lower in order to have a wide enough mag well, but I could be wrong about that.