Depending on your photography style of choice, Canon's 70-200mm f/2.8L IS telephoto lens should be in your lineup.  When I was first starting, my first L lens was the 2.8L IS zoom!  The image quality far surpassed anything my kit zoom lens had ever captured, and I really enjoyed the ability to take really high quality portrait shots.

 

Now, I actually own the f/4L IS II version of the 70-200mm.  After a night of lugging around the weight of the f/2.8 and taking shots with the dated IS system of the original, I decided to change to the smaller, lighter f/4 option  I find that the weight savings and IS improvement in the II version was better for my hikes and backpacking trips.

 

The weight is a big downside to owning this lens over the f/4 version, especially if there is any sort of hiking involved.  But I found myself not taking this lens out at all strictly because of the weight, and my hand held shots suffered when I did manage to use it.

 

If you find yourself needing a fast shutter speed for sports or low light ability, then the 2.8L is definitely the best choice.  But I think a landscape photographer doesn't really need the bigger lens and would be even better off with the f/4.  That said, I did capture some of my all time favorite images with the f/2.8L before moving on from it!  Below are some of my favorites that I've grabbed with this lens.

 

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