Simply the title. The reason I've excluded logs is because everybody chops down trees and makes planks on a daily basis, and with them this thread would be very boring.
My choice would probably be Cobblestone, simply because of my new house and the massive demands it has for things like tiles, sloped roofs and sunken floors.
For me it would have to be cobblestone. My home is a vast mountain fortess carved out of hills surrounding my original spawn point. Those tall walls were for some time comprised mainly of dirt, but little by little I sheathed 'em in cobblestone, two and more rarely three blocks deep at 'creeper level'. That's a LOT of cobble, but then I have extensive diamond strip mines. I'm lucky that the HD texture pack I use, FancyCraft by JJJas0n, has very nice cobblestone block textures.
All that gray gets monotonous. I there for use brick liberally to add a bit of welcome variety. Structure wise, brick has to be my second most used material.
I'm not much on using wood for building structures. Not yet anyway. My primary concern is blast protection. Cobblestone, stone, and brick are all bette for that. The 'bedroom' area of my main keep is wood and grass, but it's high enough in the structure so that creeper detonations shouldn't reach it...I hope. Luckily my fortress sits atop an extensive cave system with abandoned mine(s). Lots of planks, rail, and fence there ripe for the picking.
I eventually want to use a lot more obsidian. Can't get much more creeper-proof than that. I think I have about 700 obsidian blocks in storage now (thanks to small manual generator just outside my keep and an old underground farm at laval level). But at the moment I've hardly used any obisidian.
Wood usage of course goes way up with you consider weapon and tool handles, torches, and so on.
Who crafts anymore? I just order my tools and blocks via TMI Block Delivery Service! No, but in all seriousness, whenever I go on multiplayer, I get stone to get iron, but I stay with stone because stone is cheap and cost effective