.
Reviewing the already listed anniversary issues, using an online comics library, here are scans of the entire issues you can read online :
DETECTIVE 400 (the first Man-bat story, by Frank Robbins and Neal Adams. It continues and concludes in issues 402 and 407. And an O'Neil/ Gil Kane Batgirl backup story) June 1970
https://viewcomiconline.com/detective-comics-v1-0400/DETECTIVE COMICS 450 (a favorite of mine, a very pulp-hero-ish BAtman story by Elliot Maggin and Wallt Simonson. And a modest Robin backup by Rozakis/Milgrom/Austin.) August 1975
https://viewcomiconline.com/detective-comics-v1-0450/DETECTIVE COMICS 500, with stories by Brennert/Giordano, Barr/Garcia-lopez, Wein/ Aparo, Wein/Simonson, Gibson/Yeates, Levitz/Kubert, and Bates/Infantino/Bob Smith. March 1981
https://viewcomiconline.com/detective-comics-v1-0500/DETECTIVE COMICS 598-600 (highlighted by a 3-part story by Sam Hamm who wrote the Batman movie screenplay, with Denys Cowan/Giordano art, and tribute editorials and pin-up pages by a massive collection of writers and artists. 599 is a regular issue, 598 and 600 are 80-page issues. March, April and May 1989.
https://viewcomiconline.com/detective-comics-v1-0600/That kind of gives a sampling of how an anniversary issue evolved from just being a special story in a regular-size issue, to becoming a gigantic artist-jam tribute event.
And...
LIMITED COLLECTORS' EDITION C-51 (BATMAN vs. Ra's Al Ghul) by Dennis O'Neil, Neal Adams/Dick Giordano. 1977, reprintin O'Neil, Adams and Novick wok from BATMAN 232, and 242-244.
https://viewcomiconline.com/limited-collectors-edition-issue-51/BATMAN 300 by David V. Reed, and Walt Simonson/Dick Giordano, the "Last Batman Story" June 1978
https://viewcomiconline.com/batman-v1-300/BATMAN 400, by Moench, Lightle, Perez, Cullins, Sienkiewicz, Arthur Adams, Sutton, Leialoha, Kubert, Steacy, Leonardi, and Bolland. October 1986
https://viewcomiconline.com/batman-v1-400/SUPERMAN 400 by Bates and Al Williamson, Miller, Rogers, Kaluta, Pini, Janson, and Steranko . October 1984
https://viewcomiconline.com/superman-v1-400/SUPERMAN ANNUAL 11, by Alan Moore and Dave Gibbons. (1985)
https://viewcomiconline.com/superman-v1-annual-011/ACTION COMICS 600, by Byrne/Perez, Schaffenberger/Ordway, Byrne/Giordano/Beatty, Stern/Swan/Anderson, and Byrne/Mignola. May 1988
https://viewcomiconline.com/action-comics-1938-issue-600/JLA 200. by Conway, Perez / Breeding. With chapters by Broderick/Terry Austin, Jim Aparo, Dick Giordano, Gil Kane, Carmine Infantino/Frank Giacoia, Brian Bolland, and Joe Kubert. March 1982
https://viewcomiconline.com/justice-league-of-america-1960-issue-200/FANTASTIC FOUR ROAST Hembeck, Golden, Byrne, Miller, Sienkiewicz, Layton, and pretty much every Marvel artist of that era. April 1982.
https://viewcomiconline.com/fantastic-four-roast-full/AMAZING SPIDER-MAN ANNUAL 1 (Sept 1964). My vote for the singe best annual ever published, particularly of the 1960's Marvel period.
https://viewcomiconline.com/amazing-spider-man-v1-annual-001/AMAZING SPIDER-MAN ANNUAL 6 (1969) r ANNUAL 1, with additional Kirby/Ditko stories from FF ANNUAL 1, and AMAZING SPIDER-MAN 8
https://viewcomiconline.com/amazing-spider-man-v1-annual-006/
