Garden Design Application

Dear Lazyweb,

I wish someone would make a garden design program (a bit like Ikea's kitchen design one, but simpler, and online),  that I could use to, um, design my garden. Just something to get the 2D scales right. I can imagine garden enthusiasts finding this a really interesting point around which to converge a forum and maybe some pictures of their efforts. Does something like this already exist?

Thankyou Lazyweb!