Will I still be able to buy and install Lion after Mountain Lion is released?
I called 1-800-MY-APPLE and bought Lion 10.7 for only $19. I told the automated machine that I wanted to buy OS X 10.7 Lion. I was transferred to a sales representative, and he looked it up and said it was $19.99 plus taxes. I was surprised because I was expecting a $29.99 price tag. So I made him double check to make sure it was indeed 10.7 Lion and not 10.8 Mountain Lion. He said that it was for sure and that I would be emailed a PDF with a redemption code to get it.

I went through with the purchase last night (November 6, 2012) and got the email today. I was able to redeem the code in the App Store and download it from there!