I haven’t personally read any of these yet but they come with good recommendations.
The Go-Giver by Bob Burg and John David Mann
Go-Givers Sell More by Bob Burg and John David Mann
Networking Like a Pro by Ivan Misner
The Referral Engine by John Jantsch
The Power of Who by Bob Beaudine
Work the Pond by Darcy Rezac, Judy Thomson and Gayle Hallgren-Rezac.
(For more information on the principles of The Power of Who, please reference You Already Know Everyone You Need to Know)