If you want to play D1 ball, general rule is for LHP 85-88 and for RHP 87-90.
Most coaches will tell you they want guys that throw strikes and get guys out. However, the caveat is that this is true if they throw hard. They look at all the other "stuff" (ERA, K/BB, etc...), but the gun still rules. Most coaches we have talked to take the attitude that they can teach control, but they can't teach 90. They are always exceptions (Simmons?? the kid at UT a few years ago), but it is a hard row to hoe if you don't have the mph.
If you are throwing in the 70's and you can get guys out, you may want to look at D3. I think even at the D2 level, you're going to see gas.