Any time you attack with exactly one creature, every Exalted ability on the permanents you control triggers. That includes the attacking creature, if it happens to have Exalted itself.
Jeff Heikkinen DCI Rules Advisor since Dec 25, 2011
So if I have 2 creatures with exalted on the battlefield then one of them attacking alone would get 2 +1/+1 counters, right?
Wrong. Exalted does not grant +1/+1 counters. Counters give things a "permanant" power and toughness boost. All exalted does is grant a temporary power and toughness boost. If you have two creatures with exalted and one attacks alone, that creature will get +2/+2 until end of turn.