Yep, just keep killing. There are lots of places to do it, but the best place with most consistent spawns is the first camp that quests take you to - the multi-level camp on the far east side of Nagrand. I just run up and down to the spawn points and if someone else starts killing as well you can always move into the cave in the upper portion for a few minutes to keep the killing going.

Collect Obsidian Warbeads on different toons as you go - I'd collect 100 or so on each toon before looking at the rep left and trying to optimize (esp if you have some humans on your team, then you can warbead starve them to keep them at the same rep level as the others).

Oh, and finish all the quests in Nagrand (and a few in Zangermarsh) that give you rep too - probably a bit faster than the ogres and much more entertaining. That gives you a nice head start.