On a bulletin board in the lounge, we have a teacher of the week. We have slips that other teachers, and administrators can fill out and then every Monday, we select a new Teacher of the Week. They fill out a paper with some of their info (favorites, hobbies, family, sayings) and it is posted. It is a simple design, with a large sun and the teacher of week in the middle of the sun and the other nominees on the points. The slips just say nominee and reason. It is an easy way for teachers to recognize the work of others and feel appreciated.
Another thing is to do little things on a regular day. My child's class had a cookie party the other day and one mom went way over in baking cookies. So the cookies I brought in, we gave to the teachers. I put 2 in a ziplock and attached a note that said "Thank you for "chip"ping in and doing all you do! We appreciate you! From PTO" The cookies were chocolate chip. We had a lot of candy left over from a PTO night and attached one piece to a die cut star and wrote on there--You are a star. During Halloween, we started a Boo! game with all the teachers. It was just a note talking about halloween, and saying, you've been boo'ed--pass it on to two people, with a peice of candy attached. One had to go to a teacher they didn't know very well, and the other to who ever they wanted. The teachers couldn't figure out who started it and had fun with it. I was even proud to find out they included the lunchroom staff and the custodians! At our fall carnival, we had a couple go above and beyond for us, so for a couple of weeks, we just went to their room and helped with whatever they needed (copies, grading, filing, whatever). Some are just happy to get a bathroom break.
If you see them making copies, offer to do it and deliver them. If you know they like coffee, take them a cup. Give them a hug. make a card that says thank you.
It isn't the amount you spend to make someone feel appreciated. It is the act and meaning behind it.