The Challenge Magazine PDFs are excellent digital reproductions of this classic RPG magazine. The page and cover scans range from good to excellent quality (the covers may show some signs of wear from the original), and all text is fully searchable. I just wish they had gone the extra step to bookmark them as well.
This particular issue has a wealth of information for the Twilight: 2000, MegaTraveller, and Cyberpunk 126.96.36.199 RPGs, plus material for Dark Conspiracy, Call of Cthulhu, 2300, Space:1889, Shadowrun, Star Trek, and the West End Star Wars RPG. One page of this PDF is formatted upside down.