North Lake Tahoe Bootfitters
Number one rule: Buy at the mountain... they know what they're doing!
Each store carries somewhat different brands or styles, so you might need to shop around to find the boot that best fits your foot. Be honest about your skiing ability and the terrain you enjoy most. Error on the side of a softer flex, but tight fit (remember they will pack out).
Elite Feet is great. Christian is located in Squaw Valley at Squaw Creek Sports within the Resort at Squaw Creek. Bob runs the store in the Northstar-at-Tahoe Village. They carry Head, Nordica, Dalbello, and Salomon. Christian tends to carry more advanced/expert equipment. I saw that Bob ordered a few Atomic boots this year. Stay away during that 4:00 "witching hour" when they are very, very busy. It's best to make a midday appointment.
The Starthaus' focus is in race/expert. They primarily stock racing boots for adults and juniors... Lange, Rossignol, Atomic, Nordica, Fischer, Technica, and Salomon. Jim has many years of US Ski Team experience. His partner Fritz Vallant coached the U.S. women's team in the late '80s and early '90s as well as the Austrian men's tech team. This year he is Julia Mancuso's private coach. The Tahoe area has many talanted junior racers, so it is very hard to get an appointment... plan to spend a few hours even for a quick fix. (Great place to have your skis tuned, but pricey. You'll often see a U.S. Ski Team member hand-tuning your skis. They have a "hot box" as well.)
Gunner at Granite Chief in the Village at Squaw Valley is a great bootfitter. He developed a "laser platform" to make sure you are alined properly and skiing on a "flat" ski. Granite Chief has a store in Truckee with a larger boot selection, but they can easily transfer items between stores. You'll need to make an appointment with Gunner. They carry Lange, Rossignol, Tecnica, and a few others.
Cosmos has a good reputation, but I have not delt with him. Some of my racer friends have been going to him for years. He has two stores "Cosmos Custom Footwerks"... one in Truckee and the other in Tahoe City. That's maybe why you absolutely need an appointment. Cosmos carries Garmont, Atomic, Dalbello, Dolomite, Tecnica, and Fischer.
Other stores to consider are Squaw Valley Sport Shop and Porters. Each area has great bootfitters... Village Ski Loft at Incline, Bootwerks at South Lake Tahoe, etc. Just give yourself time and build a relationship with the store and bootfitter you feel most comfortable with.
Like others have written, stay away from SureFoot.
One more note, spend the money and purchase custom footbeds... they make a huge difference.
Full-time Squaw Valley Alpine Pro