Topps started issuing Stadium Club baseball cards in 1991. 1991 saw some of the first cards printed with full-bleed technology (meaning that the photograph is printed right up to the edge of the card). Although there had been some cards (minor league sets and some insert) before 1991, I think 1991 was the beginning of main-line sets being printed this way. Stadium Club from Topps and Ultra from Fleer were the first.
I also believe that the 1991 Stadium Card is the first major issue card to be printed with a high gloss and with gold foil. Both trends which pretty much took over baseball cards in the next few years. While the Ultra cards were full bleed (at least on the sides) they did not have the gloss or the foil.
Stadium Club has also been known for it's photography. The pictures were always crisp. The action shots were exciting and the posed shots were well framed.
Stadium Club was one of the first sets to produce a serious parallel set. Parallel sets of course were nothing new by 1991. Topps, Fleer and Score had produced high gloss parallels of their main sets since about 1980. In 1993, Stadium Club introduced First Day Issue cards. These had a foil seal which proclaimed that the card had been produced the first day that Topps started printing the cards. Since then we've seen an explosion of limited issue parallel cards which come packaged with the regular cards.
Over the years Stadium Club got more and more bloated with multiple parallel sets, inserts and relic cards. For whatever reason, Topps stopped making Stadium Club baseball cards after the 2003 year. I was sad to see it go but I'll admit to not being very impressed with the 2003 set. It seemed the Stadium Club designers had lost their way.
Trader Crack is starting a petition drive to urge Topps to bring back Stadium Club baseball. Go read his posting. You'll know what to do.