I started out with the kit lens on my XTI, I used that for a long time until I could afford some good glass. I purchased two lenses to get me started they were...
Why these two. Well I wanted the 70-200mm lens BAD!!!! But I wanted the more expensive version that has a lower aperature F2.8 and it has IS which is an image stabalizer inside the lens that control camera shake. I still plan to buy that lens but I had to start out with the more affordable version.
The reason for the 17-40mm was that I found it for a good deal and I thought it would be a good lens to keep on my camera all the time...my "walk around lens". It's served me well but I don't need the wide angle and again I need a lower aperature lens so I just sold my 17-40mm and I'm upgrading to the be all end all "walk around lens". It's costing me double what I paid for the other one but it is totally worth it. I can't wait to get it.
The L in the name of the lens stand for luxury. An L lens will have a red ring around the front and you can just about garauntee that it's going to take amazing pictures. Here's a link to better understand the importance of L glass. http://bui4ever.com/2008/09/canon-l-series-lenses/
I just want to have a good macro lens on hand to play with.
I'm trying to decide between the Canon-EF-50mm-f-1.4-USM and the Canon-EF-85mm-f-1.8-USM for a portrait lens. They are both great lenses but I just don't know which length I want. These lenses are not L lenses. They are fixed focal length prime lenses. They have incredible bokah, which is the blur you get in front and behind the subject. Which makes for a great portrait. I'm leaning toward the 85mm but we'll see what kind of deals I find. Lenses hold their value really well, so it's not easy finding deals.
So my run down is as follows...
24-70mm F2.8L to get the job done. It's the perfect "walk around lens". If you want to buy just one good lens this would be it.
70-200mm F2.8L for the telephoto shots. Think wedding, you can stand totally out of the way and take all kinds of candid up close pictures without anyone even knowing your around. The low aperature (F2.8) means you can use it in low light situations, like a wedding reception.
100mm macro so I can take pictures of baby feet, ears, nose, ect. or a bug on a flower. You get the picture.
85mm or 50mm F1.8 Great portrait lens and notice the aperature is REALLY low at F1.8 which makes it great for taking pictures of babies or kids indoors without studio lights.
So I hope this helps anyone else out there trying to decide which lenses to buy. It can get VERY expensive so it helps to prioritize your personal needs as a photographer. These lenses are what will work for me, there are so many more out there to choose from. Nikon carries similar lenses and there are also aftermarket lenses that are less expensive. This is totally my opinion, don't take this as fact. Do your own research and find out what's best for you. One thing you can count on as FACT though is that the lens you use does MATTER. It make the biggest difference in your pictures. That's why I'm investing in my lenses before I invest in my bigger badder camera!