If you edit c:\Program Files\EA GAMES\The Sims 2\TSData\Res\Catalog\CANHObjects\catcanhobjects.bundle.package with SimPE and change all the fields called "showincatalog" that are a 0 to a 1 in the Neighborhood Object XML filetypes, you will get access to some built-in objects that are not available in the catalog.
There are several vehicles (a junker, a cop car, two vans and a schoolbus), a waterfall, a stream, some waterfall effects, and a couple that don't seem to work.
Remember to back up your original file before editing it.
You can place the cars any way you want... pile 'em up and make a junkyard!
<* Wes *>

I haven't tired it yet, but thanks for the tip. It would be nice to
put a waterfall in my back yard ! :D

Just what Pleasantville was missing... a junkyard

These are neighborhood objects... you see them when you choose the decorations icon in the neighborhood view.
If you want them on a lot you'd have to use the MoveObjects cheat. I haven't tried them on a lot myself... maybe I should see if I can make the place a little homier by building a shack with a junker sitting in the yard.
<* Wes *>

Yeah someone over at Killersims discovered this and has them up on their site.