If your ritual does have more than one deity involved, make sure they are complementary and not at odds with one another! Also, be clear about your purpose, pay attention to ritual construction, and make sure the environment is one that would please the deities you choose.
In addition to choosing deities, you should take the time to read these sections also, to ensure your ritual achieves the purpose you intend:
To select a deity, use the selection below on the right to see which deities hold influence over what areas. Note that the Greek/Roman deities are grouped together as Olympians, since many Roman deities were simply renamed from the Greeks. In addition to pantheon and sphere of influence, you can select by weekday, planet, element, gender and name.