Several years ago, a publisher called Kitchen Sink produced three-volume sets of the Superman and the Batman daily comic strips from the early 1940s. Kitchen Sink sadly went out of business some years ago, but they left a warehouse full of unsold books behind. In 2006, a company called Sterling bought their stock and repackaged the old books in big, compilation hardbacks. So for $20 (and probably less; you can frequently find this book in the clearance section of large chain bookstores), you get a nearly 600-page hardback. It's quite heavy and awkward to read unless you can prop it on a table, unfortunately. (I reviewed the Batman book last year.)
If you do persevere with the possible discomfort of reading the collection, you'll probably enjoy the wild adventures of the original Man of Steel. Before they fleshed out his cast and backstory, and gave him a moral code, Superman was a gleefully violent strongman, who frequently extracted confessions from recalcitrant gangsters by flinging them a mile in the air or dunking them in a lake. It's also really fun to consider how important newspaper reporters were to their day and age, and how Lois Lane doesn't do herself any favors by arrogantly telling men with guns that they had better let her go, because she fully intends to expose their criminal schemes.
The stories themselves have aged very well, even if the artwork - credited to Joe Shuster, but more often handled by a number of ghost artists, some of whom are identified in the supplemental material - is certainly of its time. There's a very fun tale about visiting European royalty and a princess who falls for Clark Kent, and a great anti-war story in which Superman kidnaps two squabbling European dictators and orders them to settle their differences with fisticuffs in front of their troops. Best of all is a quite lengthy storyline in which the criminal underground puts a million dollar bounty on Superman's head, and several mad scientists take turns trying to kill him with a variety of bizarre weapons.
Actually, the thing I enjoyed the most about these stories was the sense of peaceful isolation from the rest of the DC superhero menagerie. In the 1940s, this comparatively low-powered Superman worked quite well as the planet's only superhuman, in stories where he was not known and not trusted by the police. Younger readers probably won't enjoy this as much - my son found them dated and dull - but older buyers might get a kick out of it, particularly with such a nice price point.