I have to go with a H&K USP. While the 1911 is classic, and by far the best pistol ever made, the USP offers many self-defense related advantages. It has THE most functional safety, the option of a threaded barrel, and, in the end, was designed to be a TACTICAL weapon. It also has a much higher mag capacity than a 1911. However, all this is related to it being a "combat pistol."
If money is no object, get a SIG 220 in .45 ACP or a SIG 226 in .40 S&W. The former gives you the proven stopping power of .45, but a single-stack 8-round magazine; the latter gives you a compromise between a 12-round magazine and a solid caliber. The 226, as a bonus, can be re-barrelled in .357 SIG, if that caliber appeals to you (and, anyway, flexibility is always a good thing). SIGs are built purely for business. They are extremely accurate, have excellent triggers (the new DAK is surprisingly good), and never jam. One notable feature (may be good or bad, depending on your preferences) is that they are DA/SA with a decocker; if you want to carry cocked and locked, your out of luck.
If you want the single most reliable handgun you can get, seek out a Glock. The G22 is a full-size .40 S&W, the G21 is a full-size .45 ACP. Either way, Glocks have an enviable reputation for taking whatever abuse you can dish on them and keep firing. The only downside for the Glocks is that the factory trigger takes some getting used to.
If you want a Glock but find various features of them annoying, look for a Springfield XD, which comes in the same range of sizes and calibers but is an arguably superior gun, at least in terms of ergonomics and triggers.
If you want a cocked-and-locked gun, the 1911 and its various progeny are the pistols to beat; the Springfield models are generally well-recieved, as are Para-Ordnance hi-capacity models. Kimbers are extremely nice guns (most of the time, anyway). And then there's Les Baer, Wilson Combat, and the other custom-shop guns, but the prices spiral upwards from there.
Glock 21. 14 rounds of .45 ACP in a proven, reliable package. The Springfield my turn out to be a fine gun, but it hasn't been out long enough, or tested enough to know for sure. I'll stick with Glock.
Sig 226 or 229. Both double stack mags. Tough pistol. There's a new 226 out now called the SCT (super capacity tactical). It has a 15 round magazine in .40, and a 17 in 9. Also, they make a 229 version.
I don't think you can beat a Sig for dependability.
I carry the Sig 220 Equinox as my duty weapon and the Sig 239 SAS as my off duty weapon. If I was back in the desert/Iraq, I would probably go with the Sig 220 Combat. Obviously this is my personal opinion and there are a lot of great choices out there.
To just the regular HKUSP45 full size.
In my humble opinion, it's one of the best 45's on the market right now. You might consider a Beretta PSX storm in 45, I shot one right out of the box and drilled a one hole group with it.