I have a Canon T3i with several lenses. The one I put on the camera most when I know I'm going to be taking shots of opportunity at any range is a Sigma 18-250mm f3.5-6.3 DC MACRO OS HSM that I purchased last year on eBay for under $300, including a UV filter. It looks and works like new. The equivalent zoom range on the T3i is 29-400mm which works for me for just about anything I encounter.
Sigma has a newer lens with even a wider zoom range making this one a previous generation, thus less expensive, but it has everything I need for a walk-around lens including image stabilization (OS) and a relatively large aperture. As for image quality, I've never found it to be lacking, but I realize that I am not as knowledgeable or demanding as some of our UHH brethren.
If you decide to go shopping for a second-hand lens like this, be careful of the actual configuration. I initially bought one where the price was fantastic for this lens with OS, which the description said it had, but it didn't. I was able to return it and relearned the lesson about if it's too good to be true, ....
I purchased my first DLSR camera about this time last year after experiencing a situation where my point & shoot cameras just couldn't provide the results I was seeking. I needed a camera that could provide good photographs in uncontrolled environments of everything from overall scenes down to detailed macro shots of failed surfaces. I had no brand prejudices or preferences having enjoyed cameras from Canon, Nikon and several others over the years. After much investigation and studying of reviews, I chose the Canon T3i that happened to be bundled with the basic 18-55mm kit lens.
Upon reading the manual, I quickly realized how little I really knew about photography in general and what this camera could do in particular. I've been taking classes ever since, both here in the greater Phoenix area and online. I have acquired several lenses along the way that provide the capability I need from macro and wide angle to telephoto zooms. I have never regretted purchasing the Canon T3i.
One of the best things I did was join the Ugly Hedgehog forum. There is an almost unbelievable wealth of knowledge in this forum that is willingly and joyfully shared by, for the most part, wonderful individuals from around the world. I rarely miss a day's posting and rarely have a day where I don't learn something. Welcome and enjoy!
I took Digital 102 from flying photo school last month using a $29 Groupon and was very impressed by what I learned and the personal feedback I received from the instructors. I felt that it was such a bargain that I enrolled in their Lighting 101 class this month for the full $97 price. Since then another Groupon offering was posted and I used that to enroll in their Intro to Editing class later on this year.
I had been a point-and-shoot picture taker for many years and was often frustrated by my inability to achieve the results I wanted. I purchased a Canon T3i this year and attended a local 4-hour class to learn the basics of the camera. When I originally saw the Groupon offering for flying photo school, I emailed the school to ask whether I should enroll in Digital 101 or 102. They determined that I knew enough about my camera to just go into the 102 class. By the end of that class, I could shoot good photos in Manual mode (and the various priority modes) and it was obvious that my next challenge was proper lighting. That's the class I'm in now.