Use Fudge Dice, this would give you a range of -4 to +4
If you don't know what fudge dice are they are d6's that have the symbols '+', '-' and ' ' (blank) distributed on them. You could do the samething with regular d6's with say 1-2 = +, 3-4= - and 5-6 = blank (or whatever you feel would be...