I would suggest you have a look at the Canon EF 70-300mm f/4-5.6 IS. It is the best "non L" telephoto that Canon makes other than their "DO" version which is quite a bit more expensive. If you have the money, the f/4L IS is a fantastic lens.
I'm aware of the 70-300 IS as well and have read good things about it. I didn't mention it because I thought I was throwing too many lenses out there.
I guess I wonder if the 70-300 IS would be enough of an upgrade over the 75-300 IS to make it worthwhile as opposed to living with it until I can get the L with IS. Would it be a better choice than the 70-200 w/o IS? I suppose it depends where and how you are going to use it. Better optics and faster focusing vs IS.
Too often I find myself needing more light. I'm finding it better to push the ISO since I prefer noise to blur, but noise is not so great either. The real answer would be the 70-200 F2.8 IS and even better with FF, but that's more down the road.
Like I said, I'll likely get the 85 1.8 first since it will offer good range and fast optics that will fill alot of my needs and function as good portrait lens as well.
I'm constantly learning how to pull more and more from my equipment as my skills grow, so it's all good. Even the best equipment has it's limitations. The challenge is how to make the most of it and have fun doing it!