My absolute favorite gift as a preschool teacher is one that I just received. We do an interview with the students for Mother's Day with questions such as, "What is your mom's favorite food?" and "I love my mom so much because..." One of the parents made one up for the teachers. It was so much fun to read! I wish that I had the answers from the whole class. My other favorites are drawings/hand-made cards. One mother has sent cards throughout the year that she must have written exactly what her child said. They are fantastic. Things like, "I love coming to school, and your hair is pretty," and "Thank you for teaching me about safety like not putting the scissors on my lips." I also really appreciate notes from the parents, especially when they include specifics about how we've helped their children. And just so you don't think I'm trying to sound like a saint...gift cards are also very appreciated. I get to know my preschool families well, so home baked gifts are fine with me, but I know that some people don't feel that way and throw them out. (I wish I'd known that before I baked and baked and baked for all my kids' elementary school teachers. I'm just going to pretend that they loved them.)
As far as gifts that I get multiples of every year: mugs, candles, plants/flowers. I do appreciate and use all of them, but they are something that others will most likely be giving.