and keep in mind that hybridization in plants behave a bit different than in animals
while in animals, it is the rule to have sterile offspring, in plants it is quite common to have fertile offspring (if you manage to get get offspring at all!)
As Lambelkip said, the trick is crossing within the same tribe or alliance. However, this does not always work: e.g. Cattleya x Epidendrum works in most cases; Phragmipedium x Mexipedium, does not work at all (or at least it has not worked yet!)