I recently learned that a couple of years ago Gitcorp lost the license to produce its DVD-Rom collections of various Marvel comics. I immediately bought the company's collections of Fantastic Four, Silver Surfer and Iron Man comics, to join their Avengers and Spider-Man (on 11 CD-roms) collections on my shelf.
Each disc collects scans of every issue of the spotlighted series, from the first issue in the '60's to a mid-2000's cutoff date. That represents a huge pile of comics, all squeezed into a wafer-thin disk.
Marvel has put out other collections of these comics, in a variety of formats, from their deluxe hardcover Masterworks series to their inexpensive, phone-book-thick black and white Essentials series. But no format is as comprehensive or offers more bang-for-buck than this one (with the possible exception of Marvel's subscription Website, which offers scans for a set price).
Further, unlike the other reprints, these are taken directly from the original comics. And they are not all immaculate file copies; many plainly came from private collections, and were bought off the stands by actual kids. The first issue of FANTASTIC FOUR, for instance, features the name and address of its (once?) owner stamped on the splash page. Turn the page of another comic, and you'll find that the owner used a ballpoint pen to tick off issues he bought on a house-ad checklist of titles released that month. You'll find every ad, every letters page, every distributor's mark. If the particular copy of the issue scanned has off-register printing (i.e., the colors are printed outside the lines), that's what you get. Musty smell of old newsprint aside, it's the closest you'll get to poring through actual old comics without shelling out the multibucks it would take to accumulate them.
The downside of comprehensiveness is that when a title is published for over 40 years, there'll be a lot of mediocre work -- particularly since each title had a myriad of creators. (Probably the most sustained run of brilliance is the over 100 issues of FANTASTIC FOUR that Stan Lee and Jack Kirby created from 1961 to 1970.) But there's little risk; if a particular issue disappoints, the reader can close it with a mouseclick and pick up another one.
If you can find these online or in stores, I recommend picking them up while they're still available.