well keep in mind that aperture isn't everything. what ISO where you shooting at? be prepared to shoot at at least ISO 800-1600 for most concerts. if you bump it up to that, you shouldn't have any problems making 2.8 work great, IF you expose correctly, which is very important.
honestly, if you want good glass, don't look for lenses with 'big zooms'. the bigger the zoom range, the more the lens manufacturer has to compensate for distortions of the different focal lengths, making the image quality lower. that's why pro's don't all use those 18-200mm monster range zooms (aside from the fact that they have small apertures).
for weddings: IS is really good, but not necessary. a fairly long focal length (135 or 200mm) is good also, as well as a large (f/2.8 or faster) aperture.
for portraits: there really isn't a specific requirement for portraits. if you like shallow depth of focus/field, get a fast prime.
for concerts/gigs: it really depends on your shooting style. if you like to get up close with a wide angle, get a wide angle zoom like the 17-40 f4L (i know f4 sounds large, but it's a wide angle so you can shoot at lower shutter speeds) or the 16-35 2.8L. if you like staying in the back with a longer lens, get a fast longer prime like the 135 f2.
IMO the only thing (according to what you've said) that you would really 'need' the 70-200IS for is the weddings...and even then it's not necessary. so at this point i think getting a couple primes would be a wiser choice. you could grab the 30mm 1.4 from sigma for $400 or so, the canon 50mm 1.8 for $80, and the canon 85mm 1.8 (or 100 f2 if you want a slightly longer range) for $350. altogether that's a nice little prime kit for half of what the 70-200 would cost.
most of this stuff is self explanatory...
