Have you been brave enough to pull everything out of your appliances and then clean them thoroughly? I am not just talking about the food, I am talking about the shelving and any removable parts? While this is a daunting task, it is one that doesn't need to be tackled much more than once or twice a year (depending on the average dirt level of your appliances).
The first thing you need to do is pull all of the food out. Throw out what is freezer burned or any condiments that you have used in the past 6 months or so. If you haven't used it yet, chances are that you won't. A good time to do this is when the contents are getting low (refrigerators are easier to do this way). Depending on the temperature in your area, you may want to put everything in a cooler. You will especially want to do this if your appliance is particularly dirty and will take you an extraordinary amount of time. If not, then you should be able to leave it out long enough to get everything shiny clean!
After you remove the food, you will want to pull out anything that is removable in your fridge or freezer. I like to use a mixture of bleach and hot water (1/4 cup bleach to a sink full of water) and clean everything, including the interior of the refrigerator/freezer. This will kill any bacteria that might be lingering in the appliance.
Once you have the interior of the fridge/freezer emptied of all removable parts, you will want to wash the interior of the refrigerator. You will want to look through your owners manual to make sure what you can/should use to clean. Some surfaces don't handle 'green scrubbies' very well, as they get scratched. However, green scrubbies are my preferred 'tool' and I haven't had any problems. It is easy to use and gets all of the pesky spills and drips cleaned up that have 'stuck' to the sides or rear of the appliance. So, make sure the tools and cleaners you use are 'safe' for YOUR appliance.
Once you have the interior clean and the removable parts clean - it is time to replace everything. VOILA! A clean and sparkling appliance is your reward! Luckily you don't need to do this very often - especially if you are cleaning up spills and messes as you go. Once a year is typically fine, unless you have let some accidents build up (or your children have and haven't told you!)