In Dungeon Crawl Stone Soup — in the early game, the midgame, and the endgame — which spells are most often memorized by winners?
The "Spell popularity" article on CrawlWiki contains some of the answers. This post is based on that article.
See the aforementioned wiki article: it includes much more information. This includes information on direct-damage spells, plus a link to the raw endgame spell-popularity statistics.
This post is up-to-date for Crawl 0.11. Please edit the wiki article and this post, and add to them. If you'd like me to mark this answer as community-wiki, please comment and request it.