I'm reading between the lines here, but it seems you're straying away from the zoom because of cost. You shouldn't. Many fixed focus lens' are more expensive than fully capable zooms. In the concert setting, I've found that even being able to be close isn't good enough for me...but that's me. I want/require the ability to zoom in when I want a facial expression shot, or a shot of the foot pedals, or a shot of the guitar headstock. To me, that's what's interesting about concert photography, not the boring shots that you see 90percent of the time...the waist up shot showing the instrument and the performer. OK, that's a great perspective too, but get real old real quick.
So, first thing I'd buy the 50mm f1.8 simply because it's so cheap, high quality and fast (for low light) that there's no excuse not to have one. $90 to your door.
I'd then look for a zoom in the 75-250 range. Some will say to get f2.8 or faster. Fast glass is great and it can be a gamebreaker for concert photography, but I'm not so sure you need the fastest lens on earth as your starter lens. The 50d makes up for alot with a HUGE ISO range. In fact, to me the extra ISO range on the higher priced SLRs is one of the biggest reasons to pay the extra money...that and the digic4 processor.
Since price is an object, I'd look at off brands, although Canon's lower priced lenses are pretty decent lenses. You might get a little faster lens for the same price, and similar quality, if you go with a Sigma though.
My 2 cents.
Topic: Good low light 'concert' lens for a canon 50d? (Read 8030 times)