Let me know if this is allowed or not, but uh, I'm offering some high-resolution ground textures for free (but not for commercial, illegal or offensive purposes) and they can be downloaded at my blog. I'll post a direct link to the entry instead (I'd upload them here but I'm trying to keep track of some stats on the downloads).
I attached a preview of the textures.
The downloads are here.
Let me know what you think?