When you are one of those users who have a huge usage of OpenSTreetMap tiles (i.e. to generate offline maps for your phone), the you might know that most tile providers limit the access due the huge workload.
A solution to avoid this is to set up your own server. http://switch2osm.org/ documents very well, how this can be done. Since I am working on Linux (Kubuntu) anyway, I followed this guide: http://switch2osm.org/serving-tiles/building-a-tile-server-from-packages/.
You well need quite some RAM to generate the database, but afterwards, it works quite well and you can fetch as many tiles as you want