It's a time-honoured handy hint, but worth noting if you haven't encountered it: a dab of vanilla on a cotton ball will help get rid of odours and create a subtle but pleasant fridge smell.
Photo by nlian.
Bicarb soda is often highlighted as a fridge odour solution, but vanilla has the advantage of adding its own scent. Soak a cotton ball in vanilla extract, then place the cotton ball inside an open-topped, small container such as a glass jar and put it in the back of the fridge. When you notice you don't get a vanilla-y smell anymore upon opening the door, just take the old cotton ball out and replace with a new one.
eNasha.com also suggests that you can put a few drops of vanilla in the water you use to wash out your fridge, as well.
Vanilla Scent for Your Refrigerator [eNasha.com]