Nice first shot... I like the reflection in the water.
As for zooms... the 70-200 F4 L is going to produce the absolute best photos... hands down. Hoewever, it's BIG and HEAVY, and it cost a wee bit too much for my budget.
I went with the Canon 100-300mm USM lens... great results, even when shooting handheld sports action shots. No IS however... it stops action well, ISO 800 & 1600 can be used without any real noise at all. The USM lenses are blazzingly fast to auto focus, the front of the lens does not rotate, and the full time manual focus is swee.
you might enjoy playing with the Cokin blue and gold polariser...it can turn brown merky water into blue. I had a lot of fun with it at Grand Canyone and it did the job nicely. Here is an example of what it can do:
the Cokin system is not really expensive and you can get the cokin A for about 15$, then the filter is around 20$ for the blue / gold PL.. they are very much fun to play with.