Just sharing my experience of upgrading from 18-55 kit lens. I bought Canon EOS500D cammera and 18-55 kit lens a year ago. I used it for family, friends & outdoor locations and was highly pleased with results and also for having upgraded back to SLR from compacts (5 yrs back I had film SLR).
I had one complaint that I sometime wished that kit had longer focal length. One day while portrait photographing in a room with two - three bright lights, I continously got flare from lights which were always outside the frame (kit lens does not come with any hood). So now I had two reasons to upgrade and I replaced kit with Sigma 18-200 lens. This lens comes with hood and has excellent focal range.
First new experience with the lens was that in poor light and with zoom over 100mm the auto focus refuses to work. Second issue came that by now I was reading this forum quite a bit - I learned quickly that I had bought a lens which is huge compromise on image quality (IQ). I even read in some lens testing site where the lens got only two stars in five for optical quality. With some money to spare, the situation was not acceptable. I wanted a lens which would give better IQ (& higher rating by experts)
So I went through trllion threads on this forum, read all technical litterature on net (two hours every day post dinner - otherwise I am quite busy being a manufacturing unit head) and reached conclusion to sell sigma and buy wide angle (outdoor I took majority pictures at 18mm) and to buy a 50mm prime for portraits.
I went back to camera shop where I had sold my kit & bought sigma. 30% discount on sigma was not acceptable to me and the shop guy sold me Tokina 12-24, F4 and Canon 50, F1.4.
Now Sigma does not come out of my closet. One problem I am facing is since I (& majority enthusiasts) do 99% hanheld photography, I get 1 in 5 pictures with hand shake. Second problem is that I carry around all lenses not knowing which one will be needed where. Few months have passed & both lenses are proving to be excellent in IQ. While 50, F1.4 is value for every penny/ money spent, I am not sure of wide angle (I keep repeating to my self that next holidays I will recover its value).
Off late I am now coming to view that I actually needed Canon 17-55 IS lens and cheaper canon 55-250IS. I would have used 17-55 most of the time and 55-250 once in a while when I felt the longing for longer focal length.
But the awakenning is too late now, as the shop, I know, charges 30% discount on all lenses returned.
PS: So my recommendation for all amateures is to initially go for canons 18-55, 55-250 & 50 F1.8. These are excellent lenses to begin with and low priced. Later on you can upgrade the one you use most
Reading your thread, post dinner time here, I felt I should share my happy?? experiences. Regards SS Manak