A couple of suggestions in Allen:
1) wooded area off of Ford Park East (close to Bethany and Allen Heights)
(I have pictures from here, but none I can get to now. I'll add to the thread later.)
2) Bethany Lakes Park (I have done some here with the lake in the background. There is also a large rock here for climbing photos. There is also a small waterfall in the park.)
(I have pictures from here, but none I can get to now. I'll add to the thread later.)
3) For senior photos, I often use the abandoned railroad tracks going through Allen.
4) The hiking trail in Allen Station park has several good places. (take a gobo or diffuser with you to block the light coming through the trees so you don't get "splotches")
5) Any park...
Here is a web page with all of the parks in Allen, TX
http://www.cityofallen.org/parks/parks.htm
Many of the subdivisions have a nice entry point with interesting wood or stone textures.
Best of luck to you and enjoy!!
--Alan