How do I get syntax highlighting of source code files within Quick Look back in Lion?

I don't think Snow Leopard did that by default, you most likely had a QuickLook plugin installed, such as qlcolorcode or colorqc2. You can simply install this again in Lion.

Actually, Xcode 3.x included a Quicklook plugin for source codes. With the intruduction of Xcode 4.x, such plugin has disappeared.

I have personallly tried to use qlcolorcode and colorqc2 on Lion, but both are not stable/reliable enough (slow response, sometimes missing quicklook). An updated version of the plugins would be welcome.

The Xcode 3 plugin was found at /Developer/Applications/Xcode.app/Contents/Library/QuickLook/SourceCode.qlgenerator Unfortunately I don't think this can be made to work now. :(