I'd say just invest in some higher-quality windows. If you want to go the window film route, then buy the best kind that you can. It'll last for probably a good 6-8 years before you have to replace it - at least, from what I've seen and heard. You'll have to get someone that knows what they're doing with such things to install it, otherwise it'll probably end up looking like a bubbly mess (Ever seen a good portion of custom-tinted car windows? Like that.) Also, look into some kind of blinds like Karen suggested, especially ones that have the portion facing out painted black.

If you want to get creative, try growing some large indoor plants in front of the windows. I've seen people plant vines and hang the containers above the windows. They'll filter out a good portion of the sunlight and they'll look decent while doing it, just make sure to keep them trimmed.