You could take a look at the tiles provided by MapQuest Open. They are free to use (attribution required), based on OpenStreetMap but with different rendering. Check this wiki article for more info, or you can just take a look at the MapQuest basemap by going to openstreetmap.org, clicking the Layers button on the right hand side of the map and choosing MapQuest Open. You can use MapQuest open tiles the same way you use OSM tiles e.g. http://otile1.mqcdn.com/tiles/1.0.0/map/8/126/87.png
If you're feeling adventurous you can also look at generating your own tiles. I'm afraid this is way beyond anything I've ever wanted to tackle, but there is a big community who regularly do things like this and I'm sure you'll find plenty of support and help on here as well.
Alternativey I believe CloudMade offer paid services to generate custom tiles. The ones I've seen are pretty damn beautiful as well, so it might be worth a look.