There are new manifestos ready for your stimulation at ChangeThis.com
Read and be stimulated. At your next team meeting or off-site or workshop, get the participants to write their own manifesto. This word-manifesto- and the resultant thinking can be much more stimuating then the stale work often associated with mission/mission statement. If you must have a mission statement, read this first from Michael Wade; it should get you onto the right track with some clear thinking and decent examples.