Saigas seem to be constantly out of stock everywhere I shop - must be pretty popular. Lord knows I'd be all too happy to find a Saiga-12 somewhere. Just wish somebody would start making cheap mags - it really can't cost fifty bucks to mold a plastic 10-rounder.
.22s are popular, probably even moreso these days due to rapidly rising ammo costs. A decent selection of semi-autos and bolts (I dunno how many people really buy the little Crickets at the same price point as a nice semi-auto Savage) will surely get you some business and won't be too terribly expensive to invest in stocking (I assume they go for $80-90 to wholesalers given the retail price of ~$125).
Milsurps provide a nice change of pace and a good "wuzzat?" factor for the good ole boys who've never seen a Mosin before. I can attest to the repeat effect these have - my local shop assured me that they get Makarovs in "all the time" (impossible to find in California - been craving one for years); after two months and no Mak, I'm starting to think they were pulling my leg, but darned if I don't still stop in two or three times a week to check. If they ever actually get one in and sell it to me for less than $250 I'll be a very happy customer indeed.
CZ is definitely underrepresented - all the places I've been, both local and out of town, seem to have no shortage of Glocks and XDs, but only ever have one 75B in the cases, if even that. Ditto for Kel-Tec - they're truly nice pieces for women (and men - I just see them getting more attention from the ladies) looking for a good, ultracompact CCW.
Overstocking 1911s is a sure way to immediately make me lose interest - I've been to waaay too many shops over the past year or so that have upwards of 15 different 1911s in the display case - always Kimbers and Wilsons - with maybe a Springfield GI and a RIA tossed in for the "cheap bastards," and perhaps five or ten other handguns total. Come on, at least the stacks of Glocks are different calibers and barrel lengths...
Please don't sell crap. Whenever I see a shop with a Vulcan AR for sale it makes me question their knowledge of firearms and their integrity - they're either dumb or dishonest. Neither quality engenders a desire to spend my money in that establishment.
Don't discount the cheap guns, however - Bersas and Hi-Points are inexpensive, but they (usually) work. Cheap and reliable, as you can see with your RIA sales, is a winning combination. Don't rely on high-dollar supertacticals to draw business. Stock around your demographic.
Edit: Non-Romanian AKs with mags that don't wobble like a wheel with no lugnuts would be nice too.