You're not saying what kind of party it is...but here's some suggestions:
Paper lanterns strung around
A balloon arch
Large pots filled with flowers and a tiki torch stuck in the middle of it
Rope lighting to line porches, decks along the baseboards (looks like runway lights)--put it so that no one trips, of course
Outdoor curtains, fabric to create "doorways"
Umbrellas and tables, chairs
Decorate around a tree(s) with ribbons, flowers, theme props...or use grape vine and twirl it around and insert flowers.
Mylar balloons
An outdoor firepit with seating around it
Hanging lanterns on shepherd's hooks.
Lots of candles in mason jars placed in groupings
Make your own outdoor water fountain (big pot, water pump, water plants)
