tires can be out-of-round, too. most of them are, actually, especially cheaper ones.
they're not designed for constant speeds over 10mph, so the manufacturers don't have the same standards as cars and motorcycles.
spin the tire (off the ground) and hold a crayon or chalk near the tread to see if there's a high spot.
three things can cause that.
one, is your innertubes. if you've got a fat tire and a skinny tube (like a 2.5" tire and a 2.125 tube) there'll usually be a low spot at the valve stem, because that's where the most rubber is on the tube, and it doesn't fully expand inside the tire.
(note: if you tell your local bike store that you need a fatter tube and explain why, they'll look at you like you're a total moron and probably tell you that's bs. most bike stores i've tried have been like that. just ask if they have wider tubes, and when they say "no, but..." just walk away.)
the second cause could be an out-of-round tire. buy better ones.
you might also have a "hop" in your rim. it's slightly egg-shaped and bouncing down the road. you need to true it, or find someone who can.
i build all my own wheels, and after trueing them, i mount the tires, ride them for a day or so, then re-true the wheels with the tires still on.
balancing? personally, i don't think it matters. i've been on this controversy before. harmonic vibrations in all vehicles are felt at certain frequencies, almost always most acute at 33mph. then again at 66. that's the speeds you'll notice your car's steering wheel shimmying at. accelerate, and it goes away.
same with bikes. at 33-35, my copper gas tank makes this weird humming sound, until i speed up or slow down.
but if wrapping solder around your spokes, fishing sinkers, or titanium valve caps make you feel better, knock yourself out...