Quick, easy, and inexpensive--this is great for any party (just change the color scheme!) Go to your party supply store and buy a large spool of "curling ribbon" (the kind you put on balloons).
Attach long ribbons of this from the ceiling (I like to use tape in case it falls--no unintended injuries, but have seen thumbtacks used on some ceilings) space them randomly--the effect is something like rain. I usually precut the ribbons into varying long lengths and lightly curl them (curling is optional). I try to have most "above head level" but find it fun to have a few longer ones. It gives the illusion of many helium balloons being there without the expense (or noise). If tape is too "ugly" for your tastes, try using pretty stickers to attach the ribbons. I do this throughout the party/traffic areas including pathways to the yards, and bathrooms.
I especially like using silver or irridescent ribbon for this, but have found many pleasing color combinations for different occasions (wedding, birthdays, Xmas, etc.)