its more than a balancer, its a very distinct vibration, not like a wiggle or a out of balance vibration but like a noisy vibration that feels very heavy. Its hard to explain.
if you've never replaced the u-joints... start there. it'll cost about $12 a piece and you simply remove the driveshaft (watch out for tranny fluid, hehe)remove the clips, punch out the old ones and punch in the new ones and stick in the new clips... I replaced mine and it feels like a whole new car...
Mine is doing about the samething, exept it's most prominent when I'm doing 70+, and now its doing it at most speeds so long as I'm in the 2-3500 rpm range. I'm gonna start with the u-joints, and maybe replace the whole driveshaft. Also, it olnly does it when I'm on the gas, or put the clutch in, not when engine breaking. Hopefully that's all it is, and maybe this is like what your having going on. Also, it does make a large vibration, and has a deep bass tone to it.