I missed last week, so here are a few extra.
It's not that hard a stretch to take standard decks of playing cards to simulate specialized decks that are based on the same number/suit principles. What we don't want to do is a) write on every single card, or b) consult a sheet that maps every single card to some flavor text. So we will restrict ourselves to games that require a minimum of markup.
For instance, Tichu uses a 56 card deck: 53 of the usual 13 cards in 4 suits, and 4 special cards. We can use the jokers for the four special cards, but, if your two decks have different colored backs (e.g. red and blue), we don't want the two jokers from the "other" deck to stick out.
Solution: Set aside the jokers. Mix the two decks together thoroughly, and then turn face up. Now separate into two decks of cards. Each of the two decks should be randomly constructed from the two different colored card backs.
Mark (in pencil) the special cards on the four jokers and mix them into one of the decks and play. You can use occasionally take the four aces out of the deck you are using and put them into the other deck, if you want.
Another candidate is Rook. Use the four jokers as the 14's of each suit, and then take one additional card from the other deck (say, the ace of spade with a markup) to be the rook.
For five suited games, such as Lost Cities or David & Goliath (up to 4 players or so), you can mark up one additional full suit from the second deck.