Right now, most Rangers are only accepted into groups if the group has all the other bases covered. Every other class in the game has something useful to offer a group. Rangers have high dps only.
To make a Ranger a more "useful" class, how about an AA line that will upgrade the Hawk Attack feature. The hate mitigation this spell offers is nice, but the durability of the hawk is too low. By allowing the hawk to last longer, and be immune to AoE damage like the Shaman's spirit dog would go a long way to making Rangers a valued class.
AA posibility: Increase duration by 8 seconds per point, final point makes the hawk immune to AoE effects. This will allow the hawk to be up almost all the time, and give rangers the utility to decrease group hate, something which Rangers have been asking to get for a long time. This will increase the parody of Rangers and Assassins as well, as Assassins have the hate transfer ability.