Sports Illustrated magazine began publishing in August of 1954.
Milwaukee Braves' slugger Eddie Mathews adorned the first cover. The first two issues of the magazine had inserts of "Topps cards" have made these issues very collectible. Two more issues in 1955 also contain the "Topps card" insert and carry a premium value.
SI is most valuable without a mailing label on the cover. These issues, purchased at the newsstand, increase the value by about 25%. Magazines with condition problems like water or mildew damage, loose covers will have little value, even from the 1950s.
Cover subjects will increase the interest and value in a particular issue as well. Superstars like Mickey Mantle, Michael Jordan or Ted Williams will increase the price of an issue upward. However, in the 1950s and early 60s, SI was really a "sportsman's magazine" and carried articles and covers about fishing, hunting, water skiing, and dogs. These issues can be found for $5 and less at sports memorabilia shows and on-line auction sites.
SI is great for autographs. The magazine is, by nature, a terrific collectible when signed on the cover. A Sharpie or other medium felt tip pen is best when gathering signatures. It's an honor to be on the cover and most subjects are more than willing to add their signature if they are typically generous with autograph seekers. If you locate one already signed by a deceased star such as Mantle, the autograph greatly enhances the value of the magazine.
Storing your SIs is easy. Purchase a pack of "magazine bags" and "backer boards". Slip the issues inside of these, and store them in a box, preferably indoors and away from humidity and heat.