First house, my realtor gave me a basket full of snacks (cheese, crackers, sausage, etc). I was green and didn't realize I was supposed to give her anything. But I hired her because husband was a coworker (thank goodness that didn't end up in disaster), so I kind of felt like I had already done them a favor.
Second house, my realtor offered to take photos of myself and my son to say thanks. She was just getting into photography and wanted to "practice" on us. Some of the pictures were fantastic, but there were quite a few that I never saw because she didn't like them. She now works as a professional photographer, and I actually hired her to take pictures of us again earlier this year (all of which were great). I honestly can't remember if I gave her anything at closing. Maybe a gift card?
Third house, my realtors (husband/wife/son team) took me out to happy hour and then to a really nice restaurant. I gave them a couple of bottles of some nice champagne. I guess technically it was from my dad, since he insisted on buying them. I think he was just thrilled they were able to help me find something (after he went house-hunting with me one Saturday, I think he thought it was hopeless). I suppose the champagne was kind of cliche, but I knew they would enjoy it.
The realtor I hired to sell my first house (second sale was FSBO) didn't get anything extra. But I gave her assistant, who I knew was the one who did most of the work (and who is also a good friend) a couple hundred $ gift card to Pottery Barn.
I didn't expect a gift from any of them and would not have thought twice about not getting anything. I actually think the practice is a little strange/awkward, since it is supposed to be a business transaction. IMO, the best "gift" to give them (in addition to the commission) is to refer them to friends. But I realize that gifts are common practice, so I try to play along.