I agree with MNb's line against the Vienna and Bishop's game: 4...Na5 hunting down the c4-bishop (but usually not actually taking it until White spends a tempo on a4 or a3) is extremely solid.
Against the King's Gambit Kaufman's repertoire (in the book "The Chess Advantage in Black and White") leads to solid, normal-looking positions: 1.e4 e5 2.f4 d5 3.exd5 exf4! reaching a "Modern Defence" while avoiding Bxd5 in the Bishop's Gambit.
The accepted lines with ...Ne7 also look very good when played by Adams and Sokolov but I haven't seen much published theory on them: 2...exf4 3.Nf3 Ne7 or 3.Bc4 Ne7 and Black will either break with ...d5 or transfer the knight to g6.
Against the Scotch a simple, no-nonsense way is to play the 4...Nf6 main line with ...Ba6, g6, Bg7 and short castling, and then target the e5-pawn further with moves like ...Rae8, ...d6/d5 or ....f6. For example:
1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Nxd4 Nf6 5. Nxc6 bxc6 6. e5 Qe7 7. Qe2 Nd5 8. c4 Ba6 9. b3 (or 9. g3 g6 10. b3) 9... g6 and now:
A) 10. g3 Bg7 11. Bb2 O-O 12. Bg2 Rae8 13. O-O and now Black can either enter the typical Scotch rook vs minor pieces endgame with 13... Bxe5 14. Qxe5 Qxe5 15. Bxe5 Rxe5 16. cxd5 Bxf1 17. Kxf1 cxd5, or avoid it with 13...Nb6!? as played by Kosten and Hebden.
B) 10. f4 f6 11. exf6 (11. Ba3!?) 11... Qxe2+ 12. Bxe2 Bb4+ 13. Bd2 Bxd2+ 14. Nxd2 Nxf4 15. Rf1 Nxe2 16. Kxe2 Kf7 17. Kd3 Rae8 is an unbalanced endgame, probably about equal, that was mentioned in a previous thread (see
http://www.chesspub.com/cgi-bin/yabb2/YaBB.pl?num=1260357793/all)
[Event "Budapest FS07 GM"]
[Site "Budapest"]
[Date "2006.07.08"]
[Round "8"]
[White "Kristjansson, Stefan"]
[Black "Pedersen, Nicolai Vesterbaek"]
[Result "0-1"]
[ECO "C45"]
[WhiteElo "2491"]
[BlackElo "2513"]
[Source "ChessBase"]
1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Nxd4 Nf6 5. Nxc6 bxc6 6. e5 Qe7 7. Qe2 Nd5 8. c4 Ba6 9. b3 g6 10. f4 f6 11. exf6 Qxe2+ 12. Bxe2 Bb4+ 13. Bd2 Bxd2+ 14. Nxd2 Nxf4 15. Rf1 Nxe2 16. Kxe2 Kf7 17. Kd3 Rae8 18. g4 d6 19. g5 h6 20. h4 hxg5 21. hxg5 Rh3+ 22. Kc2 Bc8 23. Rh1 Bf5+ 24. Kb2 Rh5 25. Nf3 Re2+ 26. Ka3 Be4 27. Rxh5 gxh5 28. Ng1 Re3 29. Rf1 Rg3 30. Re1 d5 31. cxd5 cxd5 32. Rc1 Rxg5 33. Nh3 Rf5 34. Rxc7+ Kxf6 35. Rxa7 Rf3 36. Ng1 Re3 37. Ra8 d4 38. Rd8 d3 39. Kb4 Rg3 40. Rf8+ Ke5 41. Rf1 Kd4 42. a4 h4 0-1