It all depends on your budget, and what type of trigger and safety system you feel suits you.
The Ruger autopistols in .45ACP are all reliable and tough,as well as relatively inexpensive. The Glocks in .45 are a bit more pricy, and some people don't like the lack of a manual safety or the Glock "Safe Action" trigger system, but Glocks are also extremely reliable and tough guns.
SIG makes the P220 and P245, which are very well made and relatively pricy. Heckler & Koch offers the USP in both full-sized and compact variants in .45ACP, although they tend to be even more expensive than SIGs and Glocks.
If you are familiar with single action triggers, and don't mind the idea of "cocked & locked" carry, there's the big world of the 1911...all sizes from longslide to ultra-compact, from manufacturers like Colt, Kimber, Springfield Armory, and Para-Ordnance. A 1911 from any of those manufacturers will cost you anywhere from $500-2500, but a nice and well-tuned 1911 is a thing of beauty and well worth the money.