I'm down to three levels remaining in Peggle to achieve Extreme Grand Master. I was struggling with the level "End of Time" for the longest time. I finally hit up Google for some tips and stumbled on a brilliant strategy that I'm ashamed I didn't think of myself.
The difficulty with Peggle is the non-deterministic nature of the shots. It is virtually impossible to line up a shot exactly the same way twice. However, there are three angles that you are able to get the same every time. The first is at the start of the level. The game always starts you out pointing straight down. If you don't move then you are guaranteed that the ball will bounce identically every time. The other two are pointing the launcher at the extreme left and right.
So the strategy for "End of Time" is to pinpoint where the bucket needs to be when you launch the ball such that you get a free ball every time. First, do this with the launcher pointing down. Keep firing this way until you have cleared every possible peg and the ball just falls straight down.
Next, point to the far left and do the same thing. For every ball you will need to keep track of the optimal bucket position to ensure a free ball. Once there are no more pegs to hit then switch to the far right and do the same thing.
This is not a perfect solution, of course, because it doesn't clear all the pegs. However, most of them will be gone and, with luck, you will still have ten balls with which to clear the rest. Still difficult, but far easier than starting from scratch.
One question remaining is what character to choose when starting the level. There really are only two viable options: Bjorn (Super Guide) or Kat Tut (Pyramid). All the others will mess up the sequence and cause you to clear pegs that might influence subsequent shots.
Bjorn is the safest as you can just ignore the Super Guide. With Kat Tut you will need to compute two sets of positions to launch each ball - one for the normal case and one when you have the pyramid active. The advantage of Kat Tut is that after you are done clearing all the deterministic pegs you might have a green peg or two left over to help you clear the rest.
This method falls apart if there are any moving objects in the level (other than the bucket). So unfortunately it won't be of help for Billions & Billions nor Beyond Reason. However, it will help with Yang Yin, which is another of the thorns in my side. Hopefully I'll get that one cleared this weekend.