[NAME, COMPANY AND ADDRESS, ex.
Jill Smith
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245]

Dear [NAME, ex. John Smith], 

Thank you so much for the generous and thoughtful gift.

I am truly appreciative of the time and effort you spent in selecting something which I have great use for! 

[HUMEROUS THOUGHT TO TIE IN GIFT, ex. The stroller will come in very handy when I bring the little one over for you to babysit.]

Best regards,

[YOUR NAME, ex. John Jones]