Leader & Liter

Ah, the lazy American T. Responsible for so many homophones. Bid and Bit would never be pronounced the same here, but Bidder and Bitter often are. Wade and Wait – two distinct pronunciations. Waded and Waited – let's just say them the same, why not?
Here's an interesting little description of the tongue tap that we (and apparently Australians) are so fond of. UK English speakers apparently wouldn't hear these words as homophones at all. Which is just as well; when we say "take me to your leader," they'll know exactly what we mean.

Dual & Duel

With an A – an adjective referring to the number two, or, more specifically, to two aspects of a single concept/item.
With an E – also refers to the number two, but only as a fight or dispute between two people.

Or, for those who prefer things that happened a long time ago in a galaxy far, far away:

Quarts & Quartz

-s – plural form of "quart," a measurement of volume.
-z – a crystalline mineral.
There is so much quartz in the earth's crust, you would measure it in tons rather than quarts.

Earn & Urn

Earn – (v.) receive payment in exchange for work.
Urn – (n.) decorative vase, often the type used for holding human remains.
If your job is too dangerous – like, oh, say, professional football in the 21st century – you may eventually earn an urn rather than a paycheck.