SELECT   PricePropertyId, PriceId, StoredDatetime, Value
FROM     PriceProperties pp
WHERE    pp.StoredDatetime = ( SELECT  MAX(pp1.StoredDatetime)
                               FROM    PriceProperties pp1
                               WHERE   pp1.PriceId = pp.PriceId AND
                                       pp1.StoredDatetime <= '20111101' )

var val = from priceProperty in PriceProperties 
                      where priceProperty.StoredDatetime == (from subquery in pricePropertyList
                                                             where subquery.StoredDatetime <= DateTime.Parse("01.11.2011")
                                                             select subquery).Max(p => p.StoredDatetime)
                      select priceProperty;

var val = from priceProperty in PriceProperties 
                      where priceProperty.StoredDatetime == (from subquery in pricePropertyList
                                                             where subquery.StoredDatetime <= DateTime.Parse("01.11.2011") &&
                                                             priceProperty.PriceId ==  subquery.PriceId 
                                                             select subquery).Max(p => p.StoredDatetime)
                      select priceProperty;