When I was Social Coordinator for my chapter, this website came in handy:
www.party411.com/themes.html

The page has different party themes suitable for indoor/outdoor...you name it. Each theme also comes with suggestions for food and decos.

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A single seed...becomes a Rose of incredible beauty.

A single grain of sand...becomes a Pearl of great worth.

A single great idea...becomes a Century of success.

Go Alpha Gam!