I have preferences based on the corporate citizenship and policies of the stores, services, or manufacturers, but outright boycotting tends to be a pain in the arse.
On my "S" list:
Wal-Mart (find 'em, fvck 'em, and flee mentality about opening and closing stores; Wal-Mart regularly closes and simply abandons stores if profits don't meet corporate goals. Also, poor HR skills.)
Best Buy--Crummy products at top-dollar prices, $30 USB cables, treating customers like crooks, and just plain acting like their sh*t doesn't stink.
Wells Fargo Bank--steadily declining quality of service from the old Norwest Bank days after Wells Fargo bought them out. Missing cash from ATM deposits on two different occasions--first time, I was unsure if it was my mistake, yet I was suspicious, so I triple counted all future cash deposits; the second time it happened, I was absolutely certain. (And to think, in the past, WF assured me that it was perfectly safe to deposit cash at their ATMs.) Out of apparent necessity due to unscrupulous, theiving bank workers, I stopped depositing my daily work tips at the nearest ATM, and started making my deposits in person during banking hours, which was a lot less convenient--but at least I got a receipt. They lost my business permanently after a teller refused to credit a green cash money depost to my account on the same business day of the deposit--told me that in order to have a deposit credited the day, I needed to use their ATM! (Norwest had always credited cash immediately, and my new credit union does). Because I didn't use the ATM, and they didn't credit my account until the next business day, my rent check bounced--my first bounced check ever. Two days later, I closed my 9 year old checking account that I'd had since I was 17, and my 15 year old savings account that I'd had since I was 11.
SprintPCS--PCS must stand for Poor Customer Service. I can't stand poor customer service--and it wasn't the fault of the poor CSRs. It was the policies--insulting, rude policies. They did everything possible to discourage you from talking to a person. For stuff that you can't take care of via their web site, wasting a lot of time on hold was mandatory. I once waited over 50 minutes for a CSR. Except for the wait, it was a 2-3 minute call for a simple problem. Astounding.