At any time during your game (when you are in the house of a Sim) press and hold B, then press Up, Left, Down, then Right, then you will hear a chime. You can then release B and within seconds, the Cheat Gnome will appear in front of your house near the sidewalk. You can then select him repeatedly for 10,000 (actually 9,999) Simoleons each time!

You can then go to grab mode and place him in the inventory, if desired. No effect, just for fun.