I'll throw out one more suggestion, the L 17-40 f4. I have used it on a crop and a full frame sensor, and I think it is great for both, and it isn't at the typical L-glass price point. It gives you a little less reach than your kit lens, but you already have a 50mm lens if you want more reach, and I think it is a nice improvement in IQ and build quality over the kit lens. Plus its a nice wide angle lens if you ever do go FF. I also have the 24-105, and I much prefer having the 17-40 on my t3i over the 24-105.
Right now you can get a 17-40 refurbished directly from Canon for under $600, which is a great deal for L glass. That is how I have bought several of my lenses, and I couldn't be happier.