Cards
One of the most obvious gifts for the serious baseball card collector is baseball cards. There are different ways you can go about acquiring these cards. You can buy cards in bulk, purchasing sealed boxes of recent cards. This gives your collector the opportunity to open several packs and root through for the winners. On the other end of the spectrum, you can try to track down the one card that your collector needs to complete a set. Speak with another collector or an employee at a collector's store for advice on finding rare cards.
Storage
Baseball cards have to be carefully preserved if they're to keep their value. You can help your collector keep his cards safe by picking up a storage system designed to protect and organize baseball cards. There are several ways to store cards--albums full of clear pages, top-loading boxes with individual card sheets or hard plastic cases for very rare and valuable cards. Find out if your collector needs storage supplies and take it from there.
Autographs
Depending on the player, an autographed card can be a valuable addition to a baseball card collection. Even ignoring the potential value of such a card, simply finding a card autographed by your collector's favorite player can be one method for delivering a top-shelf gift. Speak with a local collecting expert to find out which cards are worth checking out. Be wary of cards with fake autographs. Legitimate autographed cards come with a certificate of authenticity printed on the back.
Books
Many baseball card collectors enjoy the hobby simply for the pursuit of rare cards and the slow building of their collection. One way to enhance your collector's experience is by purchasing a price guide for baseball cards. This allows your collector to assess a total value to his collection and provides him with the knowledge he needs to negotiate a decent price on the next rare card he finds. You can also look into books that have been written about the hobby, which your collector can read in his spare time.