Thanks to all of you for your opinions. I currently own a 70-200 canon and a 10-22 canon, both great lenses as well as a few others. I guess there is no magic cure to not carry around my bag or camera backpack with me. I guess I was hoping to hear from some folks that have tried the tamron 28-300 or something in that area. When I am out and about fooling around taking shots with my 50D and my 70 -200, it is a lot of camera, sometimes people get a bit intimidated.
I know of people who have tried the superzooms and found the compromises over quality too much. With a crop frame camera you can manage to avoid some of the more extreme distortion (assuming it's a FF lens), but generally images are soft and lack contrast.
I use the Canon 28 - 300mm IS L which offers really good quality (at a huge price), but it's even more high profile than the 70 - 200mm .
The problem is that cameras like the 50D have huge pixel densities, and if you don't use top quality lenses then it's going to show in the image quality more than ever. That means either spending more on the lenses or resorting to primes.
I'd still recommend the 24 - 105mm f/4 IS L especially as you haven't mentioned a standard zoom, Ok you'll have to get a bit closer than the 70 - 200mm but it is much more low key, and it has a four stop IS system which helps in low light (so long as things aren't moving) . Obviously f/4 isn't as fast as f/2.8 but it's only one stop, made up for by the IS system, optical quality is really good, and it's a lens which will stand the test of time when you decide to upgrade to a new camera body - it also holds it's value really well if you ever want to sell it.
I agree with the 24-105 f/4 IS-L. It's definitely my goto lens for my 5D. In fact, I find that I'm pretty well covered with the 24-105 on the 5D, 100-400 L on the 40D and the cheap 50mm1.8 is there just in case.