I've found that if a holiday is coming up, I wait to see if the apps I want go on sale. I've gotten a few for cheaper/free by waiting until Easter weekend, Memorial Day weekend, 4th of July weekend, etc. If it doesn't, then I buy it.
lol.... I have learned to check the sites posted above, and just be patient.... Sometimes there is that "gotta have it" app, but most I can wait until that great sale....