I think headphones might be the single most important business purchase you can make. I splurged and bought the Bose QC15s, and no matter where I am, I can put them on and simply zone out the rest of the world. Sometimes I'll put them on, and when I come up for air the entire place will be full of people that I didn't even notice sit down next to me!

Also, like he said, have some "work music." I have 80s radio on Pandora that I've fine tuned with many a thumbs-down. I can be lethargic and unmotivated but once I sit down, put on the headphones, and play some Pandora, I can get into work zone quickly.