How to find out if an egg has gone bad (idea)
Here's a simple test: Place the egg in a bowl or pot of water. If the egg floats it is bad. If it sinks to the bottom it is good, if it stands at a 45 degree angle it's still OK. However, standing on end probably means that the egg is too old.
Source: The Joy of Cooking (Wow - I never really thought I'd use this book!)