I needed to lock orientation for one particular app, and so I wrote a
little app to do that. For good measure, I also allow it to adjust the screen timeout for different apps and to set audio boost for different apps (if you don't want the latter two features, just do menu | settings and turn them off).
Most e-reader apps do let you lock orientation, but this may be useful if you're using an app that doesn't.
To lock orientation for app X, select X from the list, choose "Orientation", and then click on "Lock". Then back out and put a checkmark beside "Activate"
You can also do the opposite: lock all apps except some selected ones. To do that, choose "Default" from the app list, "Orientation", "Lock", and then specifically unlock the app in question (I haven't tested this functionality).
The audio boost feature (like Volume+) needs Android 2.3+.
This is basically alpha quality (e.g., I kill a thread on deactivation by crashing it--not great, though it works), and test reports are welcome. And it's free and I plan for it to remain free.