Pretty sure it's not a bent rim because it's intermittent. I'm hoping it's a bad tire(s), although I would think with tires it would be happen all the time too, but I don't know. They're cheap crappy tires that were on the car when I bought. They're fine for going to and from work so. . .

I had a front wheel bearing go out at about 20k miles.

 

I also agree on the bad balance of the wheel/tire. Are you using aftermarket wheels? I have a vibration that starts out around 60, worst around 75 then past 80 it starts to go away again. Took three shops before someone got the balance right, had to use one of those road force balancing machines as opposed to a normal balance. I've never had the issue with the stock rims, but using the Gram Light 18" rims it seems to be an issue every time I get new tires.

 

I'm having that problem now, with my 18" gram lights. i'm going in to get mine balanced for the 3rd time today.

 

You might want to consider having the tires road forced balanced. Higher quality shops offer this and it can help determine if you have a bad tire.
Dan

 

http://www.gsp9700.com/
There is the link and the contact information for shops that use the balancer, we have one at our shop and it is amazingly badass.
Dan

 

I'd look into tires, its not an evo but my jeep had some bad vibration problems, mostly due to the front wheel bearings but it didn't fix it all, got some new tires and it was good to go.