If you are using Photoshop CS6 Extended (or even Photoshop CS5 Extended) you can convert your 2D layer into a 3D layer (Postcard) then you can move the camera to any position you'd like without destroying the bitmap information... you can even edit the 3D Postcard source (your file) and update it, and the 3D view will update automatically. Super simple.
More to the point, if you are doing this for a website, create an Action that just takes a selected layer, Convert to 3D Postcard and then position the Camera/Current View to where you like it, then stop and save the action. Then, for new images that you want to add to the website (that follow the same look), just open the image and run the action. Simple! All of your artwork will look the same. When you want to change the camera angle, just re-record that step in the Action. This provides you with a non-destructive and fully-editable workflow. Cheers!
More information on Photoshop's 3D features can be found at:
And example of this in action is in an answer to a very similar question:
page-1in that url shows simple rotating and stuff. It seems that I only answered/commented regarding the question in the title.