Louis = 50mm f1.4
Brian = 50mm f1.8
Difference = 0.4 and $230..!!!
Armen,
If you can still return it, I'd say send back the Quantaray lens. I bought one of their teleconverters because it was much cheaper than the Canon, but it's junk. It causes loads of chromatic abberation (colored halos around dark objects against a light background) so I olny used it once. I'd have been better putting the money towards a 'real' converter. If their other lenses are made the same way, it's easy to see where they save the money. If you have any doubts about it, take it back. Sorry
You'll probably want a 300 range in your bag though. As well as the recommendations for the Sigma, I'd say check out the Canon 70-300 IS lens. I have one of those and the image stabilizer is really helpful for shooting at 300mm hand held. I've also got a 28-105 that I tend to keep on there as my 'walking around' lens now rather than the kit lens. The kit lens has useful extra at the low end though, so I keep it around. The 10-22 is a cool lens and can produce some really interesting shots, but I've found borrowing one is good enough for the few time I really need it..!
Of course, if you can afford the L series in anything you're looking at, you won't go wrong..!
As for where to buy, check out the flea market area on Digital Grin. Here's a link to the Canon area;
House of Canon - Digital Grin Photography Forum
I bought my 28-105 from someone on there. They are all camera nuts, so they look after gear.
Other than that, the usual places that have already been mentioned. Adorama is another one I always check on the web and Calumet photo in Cambridge is an alternative to Hunts. Hunts also has a small showroom in Harvard Sq. I don't know Hunt's price policy, but Calumet will price match to bricks and mortar places.
Also, I haven't tried them yet, but the rental places ziplens.com and rentglass.com look like a good deal for a lens you only need for a particular event.
