My business partner/brother and I usually leave a nice bottle of wine at the property address (if your clients like good wine of course) and send a nice edible arrangement to their workplace! We've gotten some good feedback from both of these ideas in the past.
http://www.ediblearrangements.com - they have a lot of choices at various price points so you can pick something that fits their likes and your budget.
Hope this helps!!
Realtor, Vanguard Properties