If you build your house near your spawn point, then you can either craft a compass (http://www.minecraftforum.net/viewtopic.php?f=25&t=13134), which will point you towards your spawn point, or you can get yourself killed and respawn. If you didn't build your house near your spawn point, you can use a map rendering tool such as Cartograph (http://www.minecraftforum.net/viewtopic.php?f=25&t=13134) to render your map. You can then look at the image and find your house on it. Good luck!