LivingSocial, the US social commerce site offering city-based group-buy deals, announced today that it has secured $25 million Series B round of venture funding led by U.S. Venture Partners, with Grotech Ventures and Steve Case’s Revolution, LLC participating.

With 85 million followers, and present in 13 US cities, LivingSocial is a city-based Group-Buy site that works like Groupon, offering daily half-price city deals in local restaurants, spas, bars, retailers etc.  You sign up to a local deal feed, choose a deal and pay for it upfront online, and then receive an email/mobile voucher which you exchange for the goods/services. It’s simple, and proving to be hugely popular.

For any brands and retailers thinking of offering their own group-buy social commerce solution (and we think it’s worth considering), it’s noteworthy that LivingSocial adds a nice social twist to the Group-Buy offer; you can syndicate your purchase through social media (Facebook, Twitter et al.) and if 3 of your friends sign up for the deal, you get it for free.  Lovely. (See images below – LivingSocial makes this referral program a high profile component of their offer).

With the $25m LivingSocial deal, there’s something of a trinity of hot social commerce solutions emerging for 2010…

1. Group-Buy

2. Private Shopping Clubs

3. f-commerce (e-commerce within Facebook)

How is your brand or business planning to profit from the hot social commerce trinity?