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, Traveller, and 2300 RPGs. Two pages contain artifacts – post-it notes that weren't removed before scanning, one of which obscures a paragraph of text in an article, while the other obscures an ad, and one page of a two-page world map is inverted.