A nice telephoto zoom would help. I suggest a 70-300 zoom. I have this one for my Pentax, (which comes in a Canon mount)
http://www.amazon.com/Sigma-70-300mm-4-5-6-Telephoto-Cameras/dp/B000ALLMI8
The only thing I'm not sure about, is the autofocus. Pentax builds the autofocus into the camera, whereas I think Canon does it in the lenses. There's a slightly more expensive one with Autofocus:
http://www.amazon.com/gp/product/B0..._m=ATVPDKIKX0DER&pf_rd_r=0H92D6H081FJP6RHR4P7
These are slightly slower (aren't as good at low light) and not quite as sharp as a really good fast telephoto, but here's a shot, hand-held, at 300mm, (least sharp).
Blow-up:
No sharpening or other enhancement applied. As you see, it's pretty good for an inexpensive lens, and I've never had a problem with chromatic aberration (fringes of color, often seen on long telephotos).
I think you'd find it a nice addition to your kit. Of course if you have lots of money, there are top-rate telephotos. But the cost is surprisingly high.
There are also extreme wide-angles that are similarly expensive, if you want to do architecture or interiors.
And if you like flowers and insects, a good macro might be the next step. I don't do a lot of it, but I will take some shots from time to time. I'm cheap. I use a 100mm Phoenix manual focus (you want manual focus in a macro). It's cheaply built and probably wouldn't stand up to hard use in rough environments, but the optics are really good. Comes in your mount, I think. Here's a user's review:
http://www.nikonians.org/reviews?alias=phoenix-100mm-f35-macro-lens
If you like low-light shots, or fireworks, you'll want a tripod and a remote release. You can go cheap on the release. Don't go cheap on the tripod. The saying goes, "Good tripods should be inexpensive, light, and rigid. Pick any two."
My personal opinions, of course.