Parity & Parody

 -ity – a state of fairness, equality.
-ody – a humorously exaggerated imitation.

Than & Then

With an A – substance comparison.
With an E – time comparison.

Graham & Gram

How much does a s'more weigh?
Two grahams.

Gawd, I could keep this up all year... :)

Wade & Weighed

I'll be surprised if I Wade through my emails tomorrow and no one has Weighed in on the fact that I've basically used the same drawing of the scale for two weeks in a row... :)

Wait & Weight

Tare & Tear

-are – weight of an empty container.
-ear – rip.

Way, Weigh, Whey

As in, "There's more than one way to weigh whey."

Carat, Caret, Carrot, Karat

Carat – a measure of weight used mainly for gemstones, equal to 200 mg.

Caret – a typographic mark shaped like an inverted V.

Carrot – a plant of the parsley family, or its edible root.

Karat – a measure of the percentage of gold in an alloy, equal to 4.1667%. (Though it is worth noting that outside the US, this spelling is not used. Instead, this AND the gemstone usage are both spelled "carat.")