I daily carry a Glock 30 in an RM Lowrider IWB holster or a bellyband.
Length isn't as big an issue as height if you wear it on your waist muzzle down. The frame sticking out past the curve of your body at your waist is much more of a problem then the muzzle pointing down your leg.
Thin is good. Big bulges tend to be bad. But this can be worked around easier then something with too long a grip. If you wear your thick handgun IWB the pants hide the width OK if you have a good cover garment.
What do you like to shoot?
Ya like single actions? Thin, short 1911's are all the rage, and can work pretty well (please test anything you will be betting your life on). You can find them mainly in .45 ACP, but they can be had in 9mm and .40 from some companies.
Wheel guns work good. I'd stick with a 5 shot personally, 6 max. Those 7 and 8 shot Smiths are mighty thick.
The Sig P239 is mighty thin and compact, and can be had with a traditional double action trigger or their new DAK trigger. It comes in 9mm, .40, and 357 SIG. They also make the only PPK knock off I'd carry, the P232. Good gun for .380.
Beretta Mini-Cougars are pretty good. I can't stand their DAO triggers, but the Double/Single is tolerable. They 9mm, 40, and .45, though the .45 is a bit bigger.
H&K makes some compact handguns, but I haven't played with any really, so no suggestions on model numbers.
Kel-Tec just announced their single stack 9mm. I'm very interested, though if the triggers like their .380/double stack 9mm, it sucks.
I'm a Glock guy, but the only way to get a thinner Glock is to get the Glock 36. But they always work, don't rust, and you generally can't hurt them at all. Bone dry and full of lint they still work. Soaked in sweat, no problem. Dripping hydraulic fluid, not an issue. Good stuff.
The XD's are think like Glocks, and generally comparable size. The grip safety is a plus for some. They rust though.
Ok, I'm out of ideas.