I know of one build with the rogue-ranger that is able to get both Sneak Attack and Hunter's Quarry extra damage for a few rounds. It's really specific though, as you have to select minor action attack powers from both classes. That's about it.
I put together a fighter/avenger polearm build. Worked pretty well, but tended to be fiddly, the whole "only fighter powers marks" and "only avenger powers get oath rerolls".
It looked great on paper, but they didnt so much synergise as co-exist