I need to convert a normal voice to a more interesting sounding high tech Science Fiction computer voice.
I suppose there are dedicated tools for this task that go beyond a simple flanger?
My suggestion: focus on the performance. It's the one aspect of the sound that no piece of software can touch (or fix), so see if you can get 90% of the way there with your voice actor alone. These computerized voices all seem to have a layer of performance magic, whether it be a gentle clarity of the star trek computer voice or the sarcastic monotone of Jarvis in Ironman.
Once you've got that, there are plenty of tricks like vocoding, pitch shifting, utilizing granular synthesis, melodyne (as Andy said), and probably other specialized plugins for the task. There's also the speaker which produces the voice—not to be forgotten. A youtube search for any of these will provide tutorials.
Try to have a clear idea of the sound you're going for before you do a recording session. It will help you coach the performer(s) to give you what you need the first time around.
To create a robotic voice quickly, the trick is to duplicate your voice, and move the second voice of an image to the right. Listen to the result. Otherwise, the plug mentioned above are good. You can also use a vocoder.
Check out a YouTube vid on how they got the GLADOS voice sound for the game Portal using Melodyne. Should give you some ideas. Also if you check out the trailer for Pacific Rim you'll notice it there too!
Just to add a couple of other suggestions: the SciFi bundled Pro Tools plugin would work to get the computerised 'twang' of Jarvis, if used in moderation, or even Adobe Audition has a 'Robotic' preset for the Echo effect, I think..!