I made an Open Street Maps stylesheet.  For fun.  Check out some renders I did over London, along with links to their Google Maps equivalents for comparison.  Download the template at the bottom of the article.

Note the template refers to several Linux fonts; you may want to change those to make this template work on an exclusively Windows rendering chain.  Or, you could just try installing the missing fonts, which will probably work.  Personally I'm not the biggest fan of having to make stuff work in Linux unless I can help it, so I ended up building quite a peculiar rendering chain to get Mapnik and Apache working together while keeping the database in Windows land. (I couldn't get mod_tile to compile for Windows, so in the end I moved Apache and Mapnik to a Ubuntu VM).  Not an ideal solution for public-facing webservers, but it works.  

Shoreditch

Click here to see this in Google maps

 

Longsdale Square

Click here to see this in Google maps

 

Regents Park

Click here to see this in Google maps

St. Pancreas

Click here to see this in Google maps

Roundwood Park

Click here to see this in Google maps

Hampstead Heath

Click here to see this in Google maps

London

Click here to see this in Google maps

download

OSMTemplate.xml