5D lens questions
Hello, Tom --
I'm in much the same boat as you. I have a 30D with 28mm f/2.8 and 50mm f/1.8 primes, and am considering an upgrade to a (new) 5D MkII. Later, I would add the 85mm.
While I understand the recommendations for the 24-105, I remember your saying the weight of the Sigma f/1.4 put you off. The Canon zoom weighs 670 grams vs. the Sigma's 505 g.
Depending on which 28mm you choose*, your 28/40/85 outfit would cost just a bit more or just a bit less than the 24-105 zoom, so price-wise it's a wash. Carrying all 3 primes would weigh 815~865g, but you wouldn't always do that. When you did, two of them would be in your backpack or camera bag, not hanging around your neck.
*f/2.8 USM IS has 4 stops of Image Stabilization and weighs 50g less than the f/1.8, but costs 30% more. The f/1.8 is slightly heavier but cheaper, and offers 1.5 stops shallower DOF wide open. I would go the f/1.8.