Fashioned after the 1958 Topps insert set, two different Classic Combos cards are available.
Classic Combos Inserts
#58-KK Clayton Kershaw - Sandy Koufax
#58-KR Matt Kemp - Jackie Robinson
You can never go wrong with stickers. I really like these giant floating heads. Unfortunately, only Kershaw is available.
1967 Topps Stickers Inserts
#67S-CK Clayton Kershaw
In 1968 Topps created a test set called 3-D. It was never released widely to the public, but surviving samples have gained quite a cult following. Vintage versions sell for a huge premium today. These remind me of the old Sportsflics cards from the 80's and the Kellogg sets from the decade before.
1968 Topps 3-D Insert
#683D-MK Matt Kemp