Oh, Wedding of Spidey, Wedding of Superman. Both of those, issues leading up to 'em, and so on, and do on.
No comics are really worth selling, though, unless you own a comic store.
@Lanzy: Do you own a store? C’mon, that doesn’t count. 
@Max Torque: Oh dude, that was one I never read any issues about, but yes, it certainly is “legendary.”
Flash #105 (1st Silver Age issue)
Daredevil #1
Giant-Size X-Men #1
Incredible Hulk #182 (1st appearance of Wolverine)
Four Color Comics #178 (1st appearance of Uncle Scrooge)
Four Color Comics #386 (Uncle Scrooge #1)
Conan the Barbarian #1
Avengers #4 (1st Silver Age Captain America)
Teen Titans #1
Amazing Spider-Man #14 (1st appearance of Green Goblin)
Tales to Astonish #44 (1st appearance of The Wasp)
Incredible Hulk #2 (1st green-skinned Hulk)
Iron Man #1
Fantastic Four #52 (1st appearance of Black Panther)
Amazing Spider-Man #121 (death of Gwen Stacy)
House of Mystery #179 (Berni Wrightson’s 1st pro work)
Many many others, but those are the most “legendary” ones.
I own a copy of Godzilla vs. Barkley.
Is there a prize for the most questionable use of the term “legendary”?
First of all - drool.
Second of all - what do you mean by the Flash #105 as the first Silver Age issue - is that the first with Infantino doing the artwork or something? Why is it heralded as the first SA issue? Please note I am not doubting you at all - only that I didn’t realize there is a comic recognized as the “birth of the Silver Age” and I’d like to learn more…I guess I woulda gone with Fantastic Four #1 or something as the birth of the Silver Age, since I think of SA as mostly Marvel…
Flash #105, First Barry Allen as the Flash in his own comic. Legendary, but not generally credited as the birth of the Silver Age. That would be Showcase #4, Oct 1956, which introduced the first of a new generation of Super-Heroes after the genre all but died out after WWII and Frederick Wertham. It happened to be Barry Allen, the Flash.
Barry made several appearances in Showcase before moving to Flash, with #105, the numbering picking up where the Golden Age title ended. 105 is the first Silver Age issue of Flash.
The date for the end of the Silver Age varies, but I like to use June 1973, and the death of Gwen Stacy.
Helpful - thanks. Now I gotta go find my Amazing Spiderman #121…
I have the Cerebus compilations from when they were doing 4-5 issues per compilation - I think they cover up through what became the first large bound volume (1-25? I don’t have them at hand.)
I’ve got the first umpteen issues of Hellblazer, a couple of the early Sandman ones, some of the Alan Moore Swamp Thing (I thought I had the whole set but can’t find some of them), the full run of individual Watchmen…that’s about all I can remember. They’re mostly all in boxes somewhere.
Sigh. I -had- the first Superman / Spiderman cross-over (the huge sized one. I -believe- it was the first Marvel / DC crossover). Bought when new to quiet us kids on a long car trip. Survived until last winter when the apartment flooded and I lost a heck of a lot of books. 
Do those have any value? The one pencilled by Ross Andru? (jeez, why do I remember that??). I have one somewhere…
The scary thing is I did that Flash Fact! from memory. Mostly due to debates over Kurt Busiek’s Astro City and the Silver Agent.
I dunno. If there is a truly valuable comic, as reflected by historical (The Dark Knight) or artist (Jack Kirby), is it any less legendary if it’s in the 2nd or 3rd print?