I suppose we all have memorized more hymn stanzas than we think. Every now and then, a short phrase will pop into my head, and I'll take a few seconds to place it as a hymn I have known since childhood. The memories are more dear than the hymn, which is probably true for most people, whether they admit it or not. Just look at how often the same hymns and solos appear at wedding after wedding and funeral after funeral.
Texts aside, some melodies are utterly sublime to me. Below are a few PDFs of my favorite tunes reharmonized. I always hesitate to "mess" with some of these tunes, lest I take some of their original perfection away, but mess with them I have. Click, print, and use freely: