Creating a GIF animation from PNG files

Is there a tool to create a gif animation from a set of png files?

I tried the convert command from the ImageMagick suite, but this doesn't always succeed. Also, I have several issues with this:

I can't tell what the progress is.
No matter what I try, the -delay flag doesn't change the frame rate of the gif animation.
convert determines the frame order based upon the alphabetical order of the files names. This means that name500.png will be placed right after name50.png and not after name450.png I can fix this by adding 0's but this is annoying.