When using an encounter power to replace the basic melee attack at the end of a charge, such as daring charge (barbarian lvl 3 encounter power, phb2) does this expend the use of said encounter power? I'm thinking yes but just want to make sure.
Yes, the power is expended.
You used the power, therefore it is expended. That it was used as part of another action (as explicitly allowed by the power) doesn't change the fact that you used the power.
The only caveat would be if the power explicitly says that it is not expended (or that it is immediately recharged), but there are very few cases where that happens and I don't recall Daring Charge being one of them. The Reliable keyword is by far the most common source of that effect, but only shows up on certain martial class powers.