title: ggmap map style repository? Now that CloudMade no longer gives out APIs
body: <p>I'm not sure if this is the right place to ask this question, but does anybody have suggestions for accessing different map styles that can be used for ggmap? CloudMade no longer gives API keys to accounts which are not 'enterprise accounts'. </p>
  
  <p>From "ggmap: Spatial Visualization with ggplot2" (Kahle and Wickham), they suggest to either use Stamen or Google maps, but I'm looking for a different style than offered by these.</p>
  
  <p>Can anybody suggest a repository of map styles that could be used for ggmap?</p>
  
  <p>Cheers</p>