We've always used 60/40. Buy it from a stained glass retailer or from a craft/hobby shop.
BUY SOLID CORE ONLY, NOT “Electronic” or Rosin Core” from
hardware stores. It will make your project look yucky. Really yucky.
63/37 is a quick-set type solder. It's a little more expensive, and won't give you time to do a lot of touching-up. Stick with 60/40.
Don’t throw away the solder- re-use it, or save the scrap and bring it to a metal recycling place.
As of 2017, most 1LB rolls are around $25.
Mastercraft 60/40 stained glass solder
Studio Pro 60/40 stained glass solder
Lead-Free and 50/50 Solder
These behave differently. I had a former student come in with a roll of 50/50, to use on a project she was trying to complete in a day. The iron kept sticking, and she got frustrated. We realized that our hot irons, even at 900 degrees, were not hot enough to make the 50/50 bead like the 60/40.
As for lead-free, this type would be appropriate for making small jewelry projects. I would use a separate soldering tip for it, though, as lead contaminates
other metals, like silver, which is in lead-free solder.
For these two solders, use a temperature controlled iron, so you can make the tip hotter:
Hakko Adjustable Temp Iron
Here's a good write-up on solder types, published by Inland.
I recommend Glastar or Old Master’s. Buy only if labeled for stained glass.
Novacan Flux 8 oz.
Glastar Glasflux 4oz
And some cheap flux brushes
I use Novacan brand. It's the most common brand around for stained glass.
Novacan Black Patina for Lead
Novacan Copper Patina for Solder