Okay, maybe not in your toilet....but how about on top?
The Toilet Lid Sink has been available on Gaiam for a while now. It's such a fabulous idea, not only for saving water, but it would be great for small spaces as well.
With this model you just replace the lid of your toilet...not the entire toilet. On Gaiam's website it sells for $89-$119. That's a great deal! They claim it installs without any tools, another plus!
I really like this newer model from Caroma though. I just like the look of it better. It's the whole toilet and sink. I've seen it sold for about $399-$499, which really isn't bad at all for a toilet, sink and faucet. My only question is do you lean over the toilet or do you straddle it? It may be a little awkward. Still a fabulous idea though.