I know I'm opening a Pandora's Box of answers to these questions, but here goes:
I've had the Xsi/450D (my first DSLR) for a little over a year and I feel ready to reconfigure my lens outfit, now that I'm figuring out my shooting preferences. Right now, I mostly shoot either with the kit lens (18-55IS) or the Nifty Fifty. I did buy a used EF100-300 4-5.6 USM, but find that I have nearly no use for it - it's not wide enough at the wide end and the lack of IS makes the zoom end near unusable hand held, and I don't usually want to schlep around a tripod. It was an experiment that I found educational, but ultimately unsuccessful.
When I'm not taking pictures of my kid, I shoot mostly candid portraits and some landscapes. I recently purchased the Tokina 12-24 f/4 to cover the wide end and am now looking for some better glass in the mid to tele range that will cover most common shooting situations.
In a perfect world, I'd get either the 24-105L f4 or the 24-70 f2.8 and the 70-200L, plus a couple of fast primes (35 and 85) but that's just not within my budget.
Discovering my preference for faster (I know that f/4's not that fast, but it's not terrible), and fixed aperture lenses when possible, the questions are:
1) Can I find reasonably affordable lenses (max around $500 each- retail) with reliable IQ?
2) Do I need to have some overlap in lens coverage? I've seen a number of highly rated zooms that cover a decent range (up to 135 or 200) that seem to start at 28mm (Canon, Sigma, and Tamron all make them). Would I miss those 4mm between the end of the Tokina and the beginning of those lenses?
Begin flinging advice!
Thanks a lot.

