For once, “Flash Sale” actually means what it ought to!
A whole bunch of digital Flash collections from the Silver Age through the modern age are discounted on ComiXology this week for $5.99 each (even the long ones, like the Flash by Mark Waid and Flash by Geoff Johns collections), and dozens of individual Flash and Impulse issues are $0.99 each. Also included are Final Crisis: Rogues Revenge, Forever Evil: Rogues Rebellion, a number of Rogue-heavy issues, some Flash/Green Lantern crossovers, the main Flashpoint story, Rebirth, parts of Convergence, the Flash DC RetroActive specials, the Flash: Season Zero comic based on the TV series, the Tangent Flash issues, and more.
The later New 52 and DC: Rebirth books are on sale, but I figure you probably know already whether you’re interested in those, so I’m going to talk about the older books.
I would absolutely recommend the Flash by Mark Waid vol. 1-3 and Flash by Geoff Johns 1-3 collections. $6 for a dozen or more issues is an amazing deal, and there are some great stories in there. (Flash by Geoff Johns vol. 4 is a little more uneven than the first three, IMO.) The Manapul/Buccellato run from the early New 52 is also quite good, as are the two Morrison/Millar books with Paul Ryan and Pop Mhan (“Emergency Stop” and “The Human Race”). I’d also highly recommend the early issues of Impulse by Waid and Humberto Ramos.
You can find gems like the original Flash of Two Worlds in Flash #123, the first Superman/Flash race, “Nobody Dies” (Flash v2 #54), Wally meeting his younger self in Flash v.2 #0, the entire Trial of the Flash, and the first appearances of Jay Garrick in Flash Comics #1, Wally West and Weather Wizard in Flash #110, and Reverse Flash in Flash #139. The story with the Captain Cold Censored Flash cover is in here too. If you’re interested in the classic Silver Age Flash, now’s a good chance to pick up some of those collections as well.
If you’re on a budget, go with Flash: A Celebration of 75 Years. $6 down from $30 for this collection can’t be beat.
I wouldn’t bother with the Flash: Fastest Man Alive collections or Road to Flashpoint unless you really want a complete set.