I use Imgburn win Win 7 x64, small and free, but one disadvantage is that you cannot add files later. The one comes with Win 7 is not bad, it's integrated and convenient. I use Imgburn to burn ISO files and for others, Win 7's is simply perfect.
Another vote for ImgBurn. But I'm surprised you say that Ashampoo doesn't work...I'm going to have to give it a try since it's my favorite full-power disc burning suite.