Good manufacturers to look out for include Bauhaus Walstein, Elkhart, Trevor James, John Packer. If you have a bigger budget you could try Yamaha, Yanagisawa and others, but it may help to do some research online before diving in. Do also consider www.preloved.co.uk if you are in UK as there are several saxes available that are hardly used by people that have not really gone on to play sax - perhaps given up in their teens etc.
What is your budget? There are various options for good value deals apart from ebay, but if you want any impartial advice on particular saxes that you are considering please mention them specifically on the forum.
I have bought many things on ebay very successfully but you do need to know your stuff in my opinion.
You should be able to get a reasonable set up for under £400, including, say, a Yamaha or Rico tenor mouthpiece.
I live in Montreal but I will be going to New York for 5 days with my friends. I will try to buy one there if I will get lucky. I can spend about 600$ on a saxophone. There are places in Montreal that I can buy one for 500$ and they are good quality saxophones but the one I want is a tenor sax and usaually tenor sax is to expensive for me.
Do look up JunkDude - Dave is a helpful guy, and they do have a very good used Conn Director "Shooting Star" in the student section for $625, serviced and ready to play (dates from 1970's) - my local tech uses one of these as his professional back up horn and rates it very highly! For $600 you should be able to get a decent used Tenor Sax, such as Conn Director, Martin Imperial or similar.
Junkdude is an online retailer based in Ohio, run by Dave and Theresa. If the sax is described as being in "excellent playing condition" then I would take it at face value. Both myself and Luluna have had dealings with them.