the canon 50mm f/1.8
Sigma 28-70mm f/2.8-4
and a 70-300mm f/4-5.6
I'd be most inclined to add a wide lens to the set. One of the APS-C wide lenses would probably be the best bet. If you plan on going full frame or APS-H some day, you might consider the 17-40mm instead.
reviews i have read down play both the 70-300 and 70-200 for wildlife/sports
300mm isn't long enough for serious wildlife photography and the 70-300 won't take a Canon extender. On the flip side, if you've ever priced super telephoto lenses for wildlife, you'll seen that they are breathtakingly expensive. I looked at a short, cheap one yesterday (300 f/2.8). It was $350 just for the freaking lens hood! The lens itself was almost $4,000.
300mm will get you great zoo shots or Animal Kingdom shots. It's a nice range for hand holding. I've never owned anything longer (unless you include the not very sharp combination of a 70-200 zoom and a 2.0x extender). There have been times when I've wanted longer, but not enough to justify anything close to the expense.
For sports photography, speed is more important than reach. The 70-300 would be fine for a sunny event, but you'd start to get into trouble shooting fast action on a really cloudy day or close to sunset. Indoor shooting would also be problematic. Again, solving the problem means spending lots of money (double the price on the 70-200 to go from f/4.0 to f/2.8). IS isn't a substitute for speed when your subject is moving.
I had the old Canon 75-300mm IS (not a particularly good lens at all), and was able to get by with some sports work. Still, if my intent was to shoot a kid at indoor sporting events or after school outdoor events, it would not have worked well at all.
Like everything with cameras, you can almost aways get more/better if you are willing to spend much more and lug around more weight. The problem is that the "more" parts grow exponentially compared to the benefits. Few will argue that the 70-200mm f/2.8 is twice as useful compare to the 70-200 f/4.0. In fact, I'd bet that more than 80% of the shots I take with my f/2.8 are at f/4.0 or above. Everyone has to decide what the marginal improvement would be by going further up the price chain and whether that is worth it to them.
The problem with the reviews is that they are geared for professionals. These lenses, esp. the 70-300mm, are perfectly fine for non-pros, like me. I don't need to put the images in a magazine so I don't need the added expense for a slightly faster, clearer lens (such as the Canon "L" series). These professional level lenses are better, no doubt, but if you don't need magazine-quality exposures, you're gonna save a bundle and still have great photos.
I'll be the first to agree that "L" type lenses aren't for everyone. In addition to being very expensive, they are also a lot heavier, bulkier, draw more attention (at least the white ones do), and can be more difficult to use. Still, there is more to it than just pro's trying to get enough clarity for magazines. I'm strictly an amateur, but photography is my main hobby. I'm willing to spend more money on photo gear than most.
The main driver for the lenses that I got was actually getting the zoom range that I wanted with the minimum aperture that I wanted. Canon doesn't offer a non-L version of the 70-200 f/2.8. Sigma, Tamron, etc don't (or at least didn't) offer a 70-200 f/2.8 with IS. I wanted those features for family snapshots and was willing to put up with lugging around a 7" long, 3 pound lens. I was also willing to pay $1,000 for the extra shots that I could get and the shallower depth-of-field I could get with the f/2.8 lens.
It's all about compromises. How much money are the different features and lens quality worth to you? How much are you willing to carry around? How often are you willing to change lenses? How much will you use the lens? Because these questions are so personal, it's really hard to make lens recommendations to people.
In the old days, picking the Canon 70-200mm f/4.0 over the crummy 75-300 IS was a no brainer. The cost wasn't much higher and the 75-300 was ugly after 200mm anyway. The 70-300mm sounds like it has been hugely improved, so now you've got to think hard about which of the two makes sense for you. Do you want slightly better optics, stronger build quality, weather seals? The 70-200 f/4.0 might be your best option. Do you want a longer reach and image stabilization? The 70-300 IS might be your best option.
If you find that both are two bulky, you can get the optically inferior, much more expensive, but tiny 70-300 DO. If you aren't willing to compromise between the two, you can by the much more expensive 70-200 f/4.0 IS and a 1.4x extender.
( I swear I have NOT had too much eggnog )
