Originally Posted by
OOTCS
It's hard to really get to know Natasha from a single book, but here are some of her most important appearances, in my opinion (in order of when they were published):
1) Tales of Suspense (1964) #52, 53, 57, 60 64 -- Natasha's first appearance as an Iron Man villain, and her backstory with Hawkeye
2) Avengers (1963) #29-30 -- Natasha reunites with Hawkeye (who's now an Avengers) and switches sides
3) Avengers (1963) #36-38 -- Natasha almost joins the Avengers, but then she ends up going to SHIELD instead
4) Avengers Annual (1999) -- This is a Jarvis story, but it includes Natasha. It takes place right after the Avengers all die fighting Onslaught; she was the team leader but she wasn't on the scene when it happens, and she's dealing with survivor's guilt.
5) Marvel Knights (2000) -- An enjoyable team-up story with Natasha and a bunch of other street-level heroes, where she plays a big role
6) Daredevil: The Widow -- Daredevil (1998) #61-64 -- The story shows Natasha in both her spy and superhero roles. Art is by Alex Maleev and it's gorgeous and watercolor-y.
7) Black Widow (2004) -- There are a lot of things I don't love about this story, but it's the source of Natasha's current backstory, so it's kind of an important read, and the art is by Bill Sienkiewicz, so it's amazing.
8) Black Widow (2010) , aka Black Widow: Name of the Rose -- Art by Daniel Acuna, writing by Marjorie Liu, very good look at what makes Natasha so awesome and badass.
9) Captain America and Bucky #624 -- Despite its title, this is a Bucky and Black Widow story, with lots of flashbacks to their shared past. Written by Ed Brubaker and Marc Andreyko, art by Chris Samnee. It's adorable, romantic, sad but also optimistic.
10) Black Widow (2014) -- I don't remember a ton of this, but it kind of revolves around Natasha taking jobs and pushing away from everyone? This is right after her memory was erased in Winter Soldier (2012) (which you might want to read also, she plays a big part in it) so she's a little lost and finding her footing. Art by Phil Noto. Man, does Natasha get some great artists on her runs.
11) Black Widow (2016) -- Writing by Mark Waid, art by Chris Samnee. The story in itself is standard Black Widow stuff (red room, her past comes back to haunt her, she needs to learn to rely on other people, etc.), but the execution is very good due to the top talent on the book.
I'm missing some stuff from the 70s when she was Daredevil's partner and when she was in the Champions and from the 90s when she led the Avengers, but I think the stuff I recommended gives you a solid base. You don't have to read all of it, and you don't have to read it in order; just pick whatever era/writer/team you like best and give it a shot.