I have been working with NeoSwiff for the past few months and the product is amazing. The compiler, classes, and debugger are rock solid. The bytecode that NeoSwiff emits is highly optimized and produces swf files that are very fast. It would take you days of working with Flasm to achieve the same results NeoSwiff provides in a single compile. Better still, if you report an issue it is fixed in the next build.
http://www.globfx.com/products/neoswiff
I can't say I am good at C#, but it only took a few days to get up to speed with NeoSwiff as the compiler and debugger are solid and provide meaningful errors. Even in this early release, the product is worth a look. Considering the progress that NeoSwiff has made lately, this product is one to watch closely.
Kudos to the team at NeoSwiff. Great work!
Here is an example from Keith Peters using NeoSwiff C#:
I spent 2 hours looking through the C# source for this SWF, it is amazing. Nice work Keith!
Ted ;)
DIGG IT! 
I guess I should be completely honest here and say that I made that original fla in Flash about a year ago. The guys from GlobFX took the Flash code and converted it to C#.