Went into the T-mobile store to buy a new bluetooth headset.
I said, "Hey, do you have a discount for existing customers?" (it would have been nice if they asked me first, but hey, I'm aggressive.)
The rep, Leo, says, "what's your cell number?" Then, he credits my account $10. Not a huge amount, but a really nice gesture.
Little things, they go a long way to making customers feel appreciated.