Climbing boots adapted for crampons are perfect. Be careful not to take too small shoes. Test: leave the sole from the shoe and pose the foot on the sole. The foot must at least have 0,5 cm space at the front.
On all excursion and trekking stays you can also use solid trekking shoes.
In winter sports stores rent ski touring boots. You can also take part in the basic level trainings with your ski boots.
Plastics for Mt. Blanc or expeditions only, Nepal Extremes, Trangos, approach shoes, rock shoes. La Sportiva Trango S (medium weight, mountain boot designed with rock climbing in mind and crampon compatable), approach shoes, and a bigger boot for climbing snow peaks, like the La Sportiva Nepal or Nepal Extreme - this boot may be used on rock peaks, but the lighter rock oriented Trango S will climb better and easier.
Any good Randonee (alpine touring) boot that fits your foot well and seems comfortable. Some suggestions : Dynafit, Lowa, Nordica, Scarpa. The Scarpa Denali and the Lowa Struktura Evo are about the stiffest. You might consider getting a Raichle Thermoflex or an Intuition thermally molded liner for more warmth and touring comfort. Fit the randonee boot a little bigger than an alpine ski boot but maybe a little smaller than a plastic climbing boot. The more toe room the warmer your feet will stay on summit day, but if too big, you give up some edge control.
Any of these items can be purchased locally and the technical gear, can be rented. Another option if you are having trouble finding items in the US or want to get a better price, you can order from the web site www.cham3s.com.
Please let us know if you have any questions about equipment; for example, if you have something that you think will work, but are not sure.