Some sites on instore marketing and Point of Sale communication:
POPAI Point Of Purchase Advertising International
Salon Marketing Point de Vente
Magazine Euro PV
Retail Trends
Storecheck
Shop Floor
Retail - info for the retail professional (FR - NL)
Visual merchandising & shop design
International Sign Association
Euroshop The global Retail Trade Fair
Shop and Display Equipment Association
display Das Magazin für Verkaufsförderung und Marketing.
Display & Design Ideas.