It seems that most of the catalogs are Christian-based, so I just try to get several opinions on materials before I buy them. I just came across www.resourcefulhomeschooler.com
which does not seem Christian and has nice descriptions of all their stuff, but I haven't ordered anything from them yet so I can't tell you anything about customer service, etc.
My big suggestion is to start out slowly. Give yourself a budget and stick to it. There's a lot of stuff that sounds great out there, but you'll never use it all. I spent about $160 on a foreign language program and about $100 on other stuff (including art supplies) and my mom kicked in about $100 in books and materials --- we now have enough for about 3 years of homeschooling - and I felt I was being pretty frugal and restrained!!! It helps keep things under control and in perspective if you have a dedicated homeschooling bookshelf where all the stuff is kept. That helped me, anyway, to realize that I didn't need to keep buying new things!