Careful here, even though I agree with this idea. Unfortunately, I have found that this one doesn't work for me most of the time, as tellers or bank mgmt recently think that giftcards (of any kind) are technically a form of money, which would then possibly be seen as questionable motivation, bribery or whatever you want to call it. Sad indeed, as I don't see the harm at all in giftcards , especially if the staff at a given bank that I patronize really went out of their way for me. So then I substitute with other lovely items, such as:
1. Chocolate (of course!). I only buy the really good stuff and not the cheap crap. I actually hunt around for it.
2. Homemade goods, cookies, candies etc. This always works.

3. Something specialized and reserved for only your very best tellers. For this, I try to learn more about them over time and then get something that is unique only to them and with their initials on it, birthdate or whatever. These items usually take some preparation, creativity, time etc. Again, this is only for your very best teller, manager etc.
4. Ice cream on a very hot day. In this case, I will usually buy for the whole staff plus buy good bottled water to go with this, as some get thirsty when eating ice cream. I buy the small/tiny individual ice cream packs ($1-$2 ea) and different flavors so that they can choose. I use this one when I get something really good from the tellers and especially if it fills my coin albums. And yes, I show the better tellers my coin albums; the advantage here is that they actually will eagerly hunt for that type of coin for me (ex: wheat pennies).