If you want more ideas, study commercial packers like arma, aspr, and alike - they have lots tricks inside and some of them are really interesting. If you'd like to make it a little bit harder, try also utilize SEH - then it is real fun.
One interesting idea from one crackme I've heared of is this - it used SEH with singlestep exception; executed one instruction, overwrited the place with another one, executed it, then overwrited it with third,... quite messy to debug I think There are unlimited posibilities...
Good luck,
least

PS. look to the ^DAEMON^'s cave, here are loads of tricks...