Here's #29! Click here for the master list!
Justice League of America #29
Admittedly, the pickings are pretty slim for #29, and I think this issue, which was the second team-up between the Justice League and the Justice Society and ALSO featured the first appearance of the Crime Syndicate qualifies as the most notable #29 out there.
But I am happy to take suggestions for possible replacements!
It is not that this issue is not a very good and memorable issue, because it is!
This issue, written by Gardner Fox and penciled by Mike Sekowsky, featured the Crime Syndicate (and the first appearance of Earth-3), who get bored with their existence on their world, so travel to the Justice League's world, where the JLA seems to have a bit of an advantage. They then transfer over to Earth-3, where the Crime Syndicate has the advantage.
Earth-2 (and through Earth-2, the JSA) gets involved to be an equal battleground for the two groups.
Other notable #29s include the first appearance of the Liberty Legion in Marvel Premiere #29, two very good issues of Sandman and Swamp Thing, plus a very strong Fantastic Four issue by Kirby/Lee.
I'm open to suggestions for other notable #29s!