This will be my first year to do so, but I would love to decorate my tanks a little. I had a few ideas to try, I'll list them in case anyone is interested.
Christmas: Craft stores sell a small string of plastic lights on a thread, most of the time I see this used on home made cards, but I figured I could buy a string and put it around the tank hood for "fish sized" decorations.
I also came across this ornament:
Fireplace Aquarium Ornament | Holiday Decorations | Decorations | Aquarium - ThatPetPlace.com
Annd, since his tank is right next to my computer, I may look for one of the usb powered light up desk trees that they sold on ThinkGeek last year. :D
Halloween: I was thinking of picking up a set of those small removable window stickers to put at the top corners of the tank...although, thinking about it I'll have to see if Raphael will flare at them or not...Hmm. I may also check a craft store for "doll sized" jack o' lanterns or such to place around the the tank.
You know...if I didn't have live plants, I wonder how the fish would feel about holiday colored lighting for his tank.