As Black, I love when my opponents go for the French exchange variation. A lot of them do so OTB "to avoid theory" and to deprive Black from its beloved closed center. So, either you give up already or you you simply start working on the exchange variation, knowing it is worth it (since a lot of people will play it).
At my modest level:
1) I worked on something against the specific 4.c4 line.
It starts with 1.e4 e6 2.d4 d5 3.exd5 exd5 4.c4 Bb4 5.Nc3 (usually) Qe7+!?. White has only 3 ways of fending off the check and you can be sure the game will not be boring, it often leads to very interesting positions. With a few moves you will dare White to solve early problems properly (mostly, how to castle safely).
2) Against the more usual White's setup (Nf3/Bd3/00/c3...) I studied Alekhine's games with the following setup for Black: ...Nc6/...Bg4/...Bd6/...Nge7/...Dd7/...000. Besides Alekhine, I found GM games (including some worthy blitz games) in databases with nice attacking schemes.
In each case, it takes work. The loser side in most "exchange" variations often seems to be the one who was lazy, thinking "it's drawish anyway".
Black always has ways to unbalance the position- usually they are associated with castling long. GM Berg offers a very comprehensive Black repertoire in his 3rd French volume published by Quality Chess.