Many of the high-gravity commercial beers I taste end up coming off as boozy. What kinds of ingredients or processes will limit this flavor? I want to brew a big beer, perhaps in the 1.100 neighborhood, but I'm concerned about boozy flavors.
As alcohol levels rise in a beer, eventually you can taste it. There is just no way around that part. However as a brewer you do have control over some of the less desirable tasting higher order (molecularly complex) alcohols.
The best way to control the levels of these types of flavors is to pitch plenty of yeast, ferment on the cooler side (that also means starting fermentation on the cool side), provide plenty of oxygen up front, and be patient with the process.
The patience probably being an oft overlooked part of the process. It might take a couple months to wait out a proper fermentation.
Your yeast choice is somewhat style dependent, but look for one that attenuates really well, and plan to ferment on the cooler side of its acceptable range.
How do you feel about sour beers? I was just reading on The Mad Fermentationist that sour beers often mask their alcohol content with their other pungent aromas and flavors. And since they attenuate more than a normal brew, you get more alcohol for the same starting gravity, so take that into account as well. A 1.080 sour that gets down to 1.005 should be about the same alcohol as a 1.095 normal beer that only gets to 1.020
Beyond the sour idea, I'd suggest massive oxygenation, cool fermentation and stepped simple sugar additions. So buy an aeration system, make sure you can ferment in a controlled environment, and add simpler sugars after the primary is down with malt to get that last percent or two of alcohol without stressing out the yeast. Oh, and use a high-gravity strain of yeast as well, like WLP099 or Wyeast 3787 Trappist.