Do you jot down notes as you play the Sims to keep track of who is friends with whom? Use SimAddy to keep track of your friends and determine possible friends! I call it Sim Addy, because it's like an address book for your Sims. This simple program searches all of the Sims you've entered to find possible friend matches, based on their astrological sign. You can enter in your Sim's career information and it will display who is available at a given hour, so you know who is available before you try calling. It doesn't interact directly with the game, so you won't have to worry about it modifying important files.
You'll wonder how you ever played The Sims without it!