Spot bonuses work great (even a $10-20 gift card to Amazon was a pretty good feeling on the last project I was on). Overall praise works good, but letting them come in later on a Monday or leave early on a Friday if they really put in the work, buying lunch are also great ideas.

For myself and my colleagues, any indication that our hard work is being appreciated is usually a great motivator.

One colleague of mine was telling me about a previous project that was a nightmare, but the team pulled together and got it done. The next day they were all schedule for a follow-up meeting. When they got there, they were all handed mall gift certificates for $200 and had a bus waiting for them to take them to the mall with the rest of the day off for them to shop and socialize.