There are a lot of comic book fans among Archive readers, so I thought it would be nice to point readers in the direction - what direction is that, you ask!
Well follow me, down that rabbit hole.
When you download a comic online you'll need software that can open the files - formats like CBR, PDF or even Mobi are quite common and there are many comic book readers apps/programs online for free. So just take a browse with the search term: Comic Book Reader and you'll find a suitable program. Personally I swear by cDisplay
Comixology is an Amazon owned site and contains stuff by Marvel, DC, Dark Horse and a lot of independent houses. There are also free comics on the website so it is well worth a visit.
DriveThruComics is a great website that contains a lot of older comics as well as the new stuff.
GetComics is awesome, even if the website is a bit clunky but best of all everything here is Free to download and you can download entire runs of issues in one click. Bodacious, dude!
Internet Archive for nostalgia fans then this is the website to visit. It's comics and graphic novel section is filled to the brim with some great stuff.
British Comics is my website of choice, mainly because the archives are full to bursting with classic British comics, all of them free to download. This website is a comic historians wet dream.