In Hawkeye Vol. 1 #4, a villain helpfully tells Hawkeye, "I am a villain."
Several issues of The Mighty Thor back in the 60's had an advanced alien race send a "recorder" android along with him to an unknown galaxy to observe information. He said almost everything that was going on in the panel. Granted he was a recording android and everything, and he was probably making notes to himself, but still...
[Thor and the android get sent into a vortex of "biochemical molecules"]. Recorder: Observation: We have been plunged into a vortex of rapidly regrouping bio-versal molecules!
There's also this gem, when masses upon masses foes made of said molecules attack Thor and the Recorder:
Thor: Begone, things of evil! Not all thy masses shall topple mighty Thor! Recorder: Observation: it shall take more than platitudes to stem this mighty tide!
When the protagonist of CrossGen's Mystic finally caught on that her very obvious beau was one of the bad guys, he got one back at her:
Darrow: You always did have a fine grasp of the painfully obvious.
Sonic: Tails, what is it with you and stating the blatantly obvious?
And later on in the same strip:
Tails: Sonic! You're alive!
Sonic: And you're still stating the obvious, I see.
And in issue #115:
Tails: They... they're joining together!
Sonic: Tails, you always were an expert at stating the flipping obvious!
In one of the Summer Specials:
Tails: Sonic! He's attacking us!
Sonic: Thanks Tails, I had noticed.
Spoofed in an issue of Peter David's comic book Soulsearchers & Company, where the opening caption reads: What if Soulsearchers And Company talked like 1960's Hanna-Barbera heroes?
Janocz: Kelly! A giant tentacle is going to grab me!
Kelly: Oh no! Janocz is being grabbed by a giant tentacle!
Giant tentacle: Ha ha! I, a giant tentacle, have grabbed Janocz!
In Star Wars: Empire's End, Palpatine has an announcement to make after Han Solo has shot him: "The Corellian has killed me."
Dark Empire also contains a non-example: When Palpatine is about to pass his spirit into a fresh clone body, Luke walks in, revealing his status as a Fake Defector and his intent to destroy all the clones in the room, preventing Palpatine's perpetuation. Palpatine's response ("Very well... then I must die.") is not a case of stating the obvious, but rather a challenge for Luke to Bring It. He brings it, but it's not enough.
Young Justice dabbed into this at times when exposition was needed to point out something not clear in comic format. Of course, whenever Young Justice did something the author thought was stupid, it got mocked.
Robin: The kids... They've turned old! And those other kids are dancing out of control!
Superboy: Wow. I can tell you were trained by the world's greatest detective.