At minimum a single line in chat letting you know if you have auctions requiring your attention.

Each time you log into a toon you get a report about your auctions. This is a small and fast addon that saves the name and realm of a character as well as the number of auctions they have listed and the time the auction house was last closed. Helps you manage your auctions letting you know that a set amount of time has passed since your last visit to the auction house.