I have acquired a sculpture that is signed A. Santini. It is a nude of a male and female kissing. It is white and quite heavy and feels like marble. Does anyone know what it could be made of? Also any idea of the value.

According to one site they are made in italy from bonded carrera marble and alabaster and are hand-finished. It doesn't have an example of that piece, though.
A. Santini Sculptures (http://www.lonestartradingcompany.com/statues.html)

Someone is selling that statue on eBay for $40.
ART DECO A.Santini Statue"LOVERS" Italy 15" High - eBay (item 300327817318 end time Jul-09-09 18:48:08 PDT) (http://cgi.ebay.com/ART-DECO-A-Santini-Statue-LOVERS-Italy-15-High_W0QQitemZ300327817318QQcmdZViewItemQQptZArt_S culpture?hash=item45eceed066&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1205%7C 293%3A1%7C294%3A50)

This site has price info via eBay, if you create an account.
Vintage Nude Lovers Figurine Sculpture Signed Santini (http://www.worthpoint.com/worthopedia/vintage-nude-lovers-figurine-sculpture-signed)

From what I saw, it looks like santini statues gor for about $200-$500 each, new.