Usually, I use the cross-eye method, over longer periods without problems (probably a 90+ min movie would really be too much). IMHO, it is really the method of choice for best quality.
However, I can recommend the home-made stereo glasses described in this tutorial: http://vrtifacts.com/build-your-own-flu ... c-goggles/
They are really easy to build, so it is definitely worth a try. My glasses are shown here: http://phereo.com/image/5367cbdfcb857725120001f1
I use the glasses to show photos to friends that can't cross-view, with the advantage that they are also for cross-eye pairs.
I found that cross-eye viewing is hard to learn for some people, while others need a few minutes only.
A frame like this one may help to trick your eyes the first times (method #2): http://www.unmannedspaceflight.com/inde ... e=threaded
I added a vertical, horizontally centered needle to replace your finger used in other learning methods. After your eyes/brain learned that this works, it will be easy to switch to "cross-view mode" without the frame.