In celebration of Batman Day, Comixology is having a 7 day sale that started yesterday, which they're calling their 750 sale to celebrate the character's 75th birthday (he ages well).
A bunch of digital issues are 99cents, including what they're calling "Classics". Some of those are what I would actually consider classics like first year run issues of Detective Comics or Batman, others are are classic in the same way some of the music I grew up with is now played on "Classic Rock" stations, which is to say I have some of those issues in paper form from the days I used to buy actually comic book issues, and they're considered classic now because I'm getting old.
At any rate, I already bought most of the older Detective Comic and Batman issues and plan to read them soon-ish.
ETA: You can also get a digital copy of the original Detective Comis 27 for free, which is good since it's only 8 pages.
ETA2: The Batman Day Special Edition Detective Comics 27 is also available on Comixology, in case you are not able to make it to one of the participating comic shops, or they run out becauase you were stuck at work most of the day and some lousy kid got your copy. You'd still have to hit up a store to get those masks though.
You can see all the offerings on Comixology's site (or use the app if you have it):
And in case you don't normally go there, io9's deals page also has links to an Amazon Kindle sale.
You can get the Kindle Edition of a few collections for $2.99. Which brings me to another reason I mention this. I already have most of those stories on paper, except the New 52 ones because I haven't bought anything to do with it. The same collections are also available on Comixology for the same price.
So please let me know if these stories are worth the read, especially at $2.99. Thanks in advance for any replies to this.
Court of Owls
The Black Mirror
Batman: Earth One