Isaac Asimov could sure put together a mean anthology, and this has to be one of his best. There are so many great stories in this book that I won't list them all, but my favourite has to be Jack Williamson's classic Wellsian tale "The Moon Era". This is an absolute gem of a story, which featured a complex and sympathetic alien protagonist (the "mother") several years before the first appearance of Tweel, in Stanley G. Weinbaum's classic SF short story "A Martian Odyssey". But, then, Jack Williamson was often ahead of everybody in SF, wasn't he? :)
With what seems to be a recent resurgence in popularity of classic Golden Age and pre-Golden Age SF and the growth of specialist SF publishers such as Haffner Press, who concentrate on collectible editions of golden oldie classics from the same era, BEFORE THE GOLDEN AGE is an absolute "must have" for all fans of this kind of SF.
This is one of my favourite SF anthologies, EVER. A mammoth hardcover of over a thousand pages, which is broken up into three (sometimes four) books when published in paperback, this book collects some of the best SF stories of the 1930s. Bursting at the seams with nostalgia and sensawunda, I'd recommend this gem of an anthology to all fans of early SF.
This huge hardcover, the original edition, is the most desirable for true collectors (and I'm totally thrilled to have it). But if you can't find it (or afford the expense), track down the much cheaper paperback volumes, which seem to be found easily enough on Amazon or Ebay. You won't regret it.