Since you are using photinia (I assume red-tip photinia?), I also assume you want a tall, evergreen hedge?

What about adding Podocarpus? Thuja 'Emerald Green' - AKA Emerald, Emerald beauty or Smaragd - grows to 15-20' x 3-4'. T. 'De Groot's Spire' is shorter and skinnier. 'Sky Pencil' holly is too slow and narrow to be a major player, but might provide an accent. Arizona Cypress has bluish needles, and cultivars that are narrow, as does Italian Cypress, which is more green - both may grow too tall with time. There are columnar Junipers as well, growing from 12-19' x 3-12', depending on the selection. Cephalotaxus, Japanese plum yew, grows to 10-15' x 10' wide, takes pruning very well, and has smaller and narrower cultivars such as 'Stricta', 10' x 6-8'.

Get hold of a copy of the Sunset Garden Book - either look in a good book store or try your library, if you don't have or want to buy your own - and look in the front of it to see what they list for hedge trees/shrubs.