Expertise, Armor Penetration, etc....Follow

So the days of attack power and strength are over it seems. Now I have a litany of new stat enhancements to choose from, and I can honestly say I have no idea how to use them to maximize output.

Are there any tools or formulas that help in determining when Expertise, Armor Penetration, Haste, etc are pfereable to good 'ol AP and STR?

One thing I've really noticed with my gear "upgrades" is that my Crit chance is plummeting as I replace old arena gear, and my Arms spec that was very effective early in northrend seems to be losing it's luster. So if I'm trading away the burst from crits, do I need to be targeting normal damage with boosts to things like haste and Armor Pen?

A little help, please