Traps and alternate variations in the Spanish Game Which opening traps do the Spanish Game (ruy lopez) offer - and are there experimental/alternate variations (apart from non 3. ...a6 variations) to the opening that could be forced on either side of the board?
I don't play the Lopez, so I can't answer the part relating to experimental variations, but I can list some of the common traps:

Tarrasch Trap in the Open Variation

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. 0-0 Nxe4 6. d4 b5 7. Bb3 d5 8. dxe5 Be6 9. c3 Be7 10. Re1 0-0 11. Nd4 Qd7?, White wins a piece:

[FEN "r4rk1/2pqbppp/p1n1b3/1p1pP3/3Nn3/1BP5/PP3PPP/RNBQR1K1 w - - 0 12"]



   12. Nxe6 Qxe6 (or fxe6) 13. Rxe4


Tarrasch Trap in the Steinitz Variation

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 d6 4. d4 Bd7 5. Nc3 Nf6 6. 0-0 Be7 7. Re1 O-O, White wins a pawn:

[FEN "r2q1rk1/pppbbppp/2np1n2/1B2p3/3PP3/2N2N2/PPP2PPP/R1BQR1K1 w - - 0 8"]



   8. Bxc6 Bxc6 9. dxe5 dxe5 10. Qxd8 Raxd8 11. Nxe5


Mortimer trap

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. d3 Ne7 5. Nxe5?, Black wins a piece for 2 pawns:

[FEN "r1bqkb1r/ppppnppp/5n2/1B2N3/4P3/3P4/PPP2PPP/RNBQK2R b KQkq - 0 5"]



   5...c6 6. Nc4 d6 7. Ba4 b5 8. Bxb5 cxb5


Noah's Ark Trap

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 d6 5. d4 b5 6. Bb3 Nxd4 7. Nxd4 exd4 8. Qxd4?, Black wins a piece:

[FEN "r1bqkbnr/2p2ppp/p2p4/1p6/3QP3/1B6/PPP2PPP/RNB1K2R b KQkq - 0 8"]



   8... c5 9. Qd5 Be6 10. Qc6+ Bd7 11. Qd5 c4


Mate in the Exchange Variation

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Bxc6 dxc6 5. O-O Bg4 6. h3 h5 7. hxg4?, Black has good mating chances:

[FEN "r2qkbnr/1pp2pp1/p1p5/4p2p/4P1P1/5N2/PPPP1PP1/RNBQ1RK1 b kq - 0 7"]



   7... hxg4 8. Nxe5 Qh4 9. f3 g3 lead to mate


Mate in the mainline

After 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. Nc3 Bc5 6. Nxe5 Nxe5 7. d4 Bb4 8. dxe5 Nxe4 9. Qd4 Nxc3 10. bxc3 Ba5?, White has a mating attack:

[FEN "r1bqk2r/1ppp1ppp/p7/b3P3/B2Q4/2P5/P1P2PPP/R1B1K2R w KQkq - 0 11"]



   11. Ba3 b6 12. e6! Qf6 13. Bxd7+ Kd8 14. Bc6+! Qxd4 15. e7#


Suggestion for the community: should we turn this answer into a community wiki? I realise I've listed only a handful of traps.