Solar cookers which you can buy are a great. Most of them get to high temperatures and are made from durable materials with specialized parts which the typical DIYer can't make. The same principles carry over from homemade cookers to premade cookers. Tips like cutting the ingredients smaller for faster cooking or using black cooking containers instead of shiny ones hold true whether or not a cooker is manufactured or not.
Since there are hundreds of solar cooker manufacturers worldwide, it would be unfair to highlight just a few of them. (SJSC does not endorse any particular brand of solar cooker.) So instead of getting a list of brands, you will get a list of questions. When shopping for a cooker, ask yourself some of these:
Is this a reliable seller?
What is the warranty?
Can I buy parts if something breaks?
Do I want to buy this second hand?
Do I want to cook with high heat, or do I want a slow cooker?
Do I have room to store this?
Do I need this to be portable? If so, how much does this weigh?
Is this easy to clean?
How durable is this?
What have others commented about this cooker?
How many people am I cooking for? (How big does this need to be?)