Dump the 50/1.8 for the 50/1.4, IMO. It's a vastly superior lens.
Canon makes a 17-40 f/4L that pairs nicely with the 70-200 f/4L. I'd like to see an f4/L complement to the 24-70 f/2.8L (my favorite lens), but I won't be holding my breath.
Ignore third-party lenses, IMO.
Now I'm wondering, are these good choices? Which one should I get first, second, and third? Should I get a Speedlite as well?
What are you shooting? How are your light conditions? What's your environment? What's your budget?
Generally, the shooters I know lean toward a basic kit of 3 or 4 lenses:
- Wide-angle to short-telephoto for a "walk-around" lens.
- Super-fast prime.
- Decent telephoto lens.
- A "specialty" lens, filling some other gap in their kit.
After 3 years of shooting on borrowed and rented glass, I settled on a four-lens kit (EF-S 10-22, EF 24-70 f/2.8 L, 50 f/1.4, and 70-200 f/2.8) that fits nearly every photographic need I have.
When I upgrade to a full-frame body in a few years, I'll dump the 10-22 and pick up a 16-35 f/2.8 L (or its replacement, if that happens) and keep the same focal lengths but improve image quality and aperture choices.
I'd like something like the Sigma 30mm f/1.4, but I don't like third-party lenses. I'd also like to pick up a 1.4x or 2x EF extender to go with my 70-200, but I won't be buying them any time soon.