Almost every brewing strain in existence today was at one point part of a mixed culture. When experimenting with mixed culture, a good strategy is to mix flocculent strains with non-flocculent strains. A good place to start liquid yeast-wise is Wyeast 1968/WLP002 and Wy1007/WLP036. This combo gives a brewer a mixed culture that produces good flavor, attenuates well, and top crops. While I do not care for Nottingham or Windsor when used as single-strain cultures, they go together like peanut butter and jelly.