As a visual artist, it's basically my job to conceptualize seasonal decors and at times, just plain old store visual merchandising. Whenever there's an event coming and I need to present design proposals, I always check out
www.vmsd.com. It has lots of window display designs and props useful for all occasions. Architects and interior designers will really find this site helpful since it also has fixtures, graphics & signages etc.
Another really useful site for visual design is
http://www.btmteam.net. It's actually an advertising agency that does virtual tour programs, graphic designs and etc. for companies in their events or promotions.
The great thing about this site is that it provides samples of visual merchandising in 360 degree views which allows you to really navigate the store like Macy's, and know where the campaigns are laid out or how the products are displayed.
Macy's RTW