Black has the following, ranked in approximate order from best to worst.
5... Ba5:
This is the "Normal Variation". It had been considered best for many years, but is now slightly out of fashion. b6, not a5, is the square the Bishop is headed for, so that he can play ... Nc6-a5, which would attack the c4 Bishop and a Queen on b3.
5... Bc5:
This variation was popular in the 19th century, but seems bad at first glance, as White can play 6. d4, with a large pawn center attacking Black's minor pieces. However, this variation might be the best way to handle the Evans, as it is not a loss of tempo to play ... Bb6, and the Bishop at c5 does not take a5 away from the Knight. If you play the Evans, you will probobly see this variation the most often.
5...Be7
This is considered a relatively safe way of handling the Evans. It has gained quite a bit of attention since Kasparov-Anand, Riga 1995. The Bishop at e7 does not take away the a5 square, is fairly active at e7, and can't be attacked by White's center. However, the Black Queen can not protect f7 with ... Qe7 or ... Qf6.
5... Bd6!?
This is the strange looking Stone-Ware Variation. Black's idea is to strongpoint at e5. However, White can often trade on this square, and since Black will recapture with a piece, White can play f2-f4 in some lines. Also, the Bishop is blocking the 'D' pawn, so Black's development will be very slow, which is not a good idea in the Evans!
5... Bf8?!
This, the Mayet Defense, was a favorite of Steinitz. It also aims to strongpoint at e5 with ...Qe7, ... d6, ... g6 and ... Bg7. It is considered dubious and not very promising.
5... b5?
With this, Black is saying "I don't know why you gambitted you 'B' pawn, but I will do the same". This is simply not good, as Black can't play c6 and d5.
5... f5?
In this variation, Black sacrafices a piece to try and take over the center. This was analysed as VERY poor long ago.
After:
4. b4 Bxb4
5. c3
Black has the following, ranked in approximate order from best to worst.
5... Ba5:
This is the "Normal Variation". It had been considered best for many years, but is now slightly out of fashion. b6, not a5, is the square the Bishop is headed for, so that he can play ... Nc6-a5, which would attack the c4 Bishop and a Queen on b3.
5... Bc5:
This variation was popular in the 19th century, but seems bad at first glance, as White can play 6. d4, with a large pawn center attacking Black's minor pieces. However, this variation might be the best way to handle the Evans, as it is not a loss of tempo to play ... Bb6, and the Bishop at c5 does not take a5 away from the Knight. If you play the Evans, you will probobly see this variation the most often.
5...Be7
This is considered a relatively safe way of handling the Evans. It has gained quite a bit of attention since Kasparov-Anand, Riga 1995. The Bishop at e7 does not take away the a5 square, is fairly active at e7, and can't be attacked by White's center. However, the Black Queen can not protect f7 with ... Qe7 or ... Qf6.
5... Bd6!?
This is the strange looking Stone-Ware Variation. Black's idea is to strongpoint at e5. However, White can often trade on this square, and since Black will recapture with a piece, White can play f2-f4 in some lines. Also, the Bishop is blocking the 'D' pawn, so Black's development will be very slow, which is not a good idea in the Evans!
5... Bf8?!
This, the Mayet Defense, was a favorite of Steinitz. It also aims to strongpoint at e5 with ...Qe7, ... d6, ... g6 and ... Bg7. It is considered dubious and not very promising.
5... b5?
With this, Black is saying "I don't know why you gambitted you 'B' pawn, but I will do the same". This is simply not good, as Black can't play c6 and d5.
5... f5?
In this variation, Black sacrafices a piece to try and take over the center. This was analysed as VERY poor long ago.