However, I think your wedding theme shouldn't be dictated by any of the above -- it should be a reflection of your personality (and your future husband's of course!) The budget and everything else are factors you can work on after you've selected your theme.
In no particular order, these are the 5 themes I like:
1. Glitz and Glamour: This is a side effect of us watching the Great Gatsby. 1920's is one of my favorite decades in fashion history -- it was a time of wealth and prosperity, of clandestine excess and partying.
2. Victorian Couture: It's all about romance, beauty, and chivalry. It makes me giddy just thinking how men courted women during that time -- reciting poems, sending love letters, serenading... the list goes on.
3. Fire and Ice: This one is based on fantasy novels. Think -- Styles in High Garden or in Westeros. Then, the venue would be strewn with white and golden roses.
5. The Girl on Fire: And of course, who wouldn't want to see a scene similar to the utopian Capitol in Hunger Games? Just imagine how vibrant it would be.