My car is coming up on 90k miles. I want to change the spark plugs but I wanted to ask the forums which spark plugs will yield the best mpg?? Also should I change the o2 sensors?

I'm no expert but your spark plugs will not determine your hp or mpg. If you change them, I'd personally go with the OEM iridium platinum tipped plugs. These cars use ignition coils and basically the spark hits the coil and the coil delivers the proper "ignite" for the pistons. If your plugs are bad or not sparking properly they will cause strain on the coils and eventually they will fail too. But, in short, the plugs are either sparking or they're not.

Changing or cleaning the o2 sensor could effect your mpg, but unless you're getting noticeably horrible performance or mpg's I wouldn't mess with them. They are very sensitive and are not cheap to replace.

New O2 sensors would honestly be better. I am replacing my stock ngk iridium with Denso double platinum today. Ultimately the only difference between iridium, platinum, and copper is longevity in That order.

Your plugs are worn, so you will feel a bump in hp and probably get an extra mpg or two (especially if you're an 03-04). But that's only because they're worn. New plug for new plug, however, there is no magic mpg plug. It's just about longevity of material like Urban said.