Thanking Client

Hi,
Is there an appropriate action (you know how realtors and car dealers send 
flowers to their purchasing clients?) when finishing a site for a 
client?  (One who profusely thanks you for all your hard work, etc.)
These people have shown great consideration in getting materials to me and 
helping in any way they could.  They also had one particular person who 
managed the entire project and who kept in contact with me about my needs 
concerning pics, logos, etc.
I would like to say thanks back....how?
How does everyone handle this?

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