Working as a full time professional magician, I perform at countless parties throughout Hampshire, Surrey and Berkshire each year, many of which are themed!
Here are the top 5 (in no particular order) party theme ideas that I have come across :
1 - Casino Parties - Over the past year, casino parties have, hands down, been the most common theme for a party. Due to its popularity, it's easy to find plenty of props and decorations in party shops and online! You can hire a variety of casino tables (poker, black jack, roulette etc.) with staff, or you can buy your own card/roulette tables and host the games yourself.
2 - Ties and Tiaras - If you and your guests love to dress up for an occasion, this is a fantastic party option! It leaves a lot of freedom for all your guests, so they won't have to buy a costume for it that they will only wear once. It also leaves a lot of options for party entertainment ideas, without the restrictions of an obscure theme.
3 - Masked Balls - The 'dress to impress' masked ball theme is timeless and enjoyed by all ages. There is a lot of fun to be had with the masks, you can chose a colour scheme, or let the guest chose any mask. Remember to have lots of spare masks for guests who 'forget' to bring theirs!
4 - Films - These are a great way to put your personal taste into the party. Chose your favourite film, and theme the decorations and dress code around it. You can give your guests particular characters you want them to dress up as on their invitation, or let them chose who they like. A few film themed parties I've performed at recently are, Grease, James Bond, Alice in Wonderland and Rocky Horror!
5 - Fancy Dress - These parties are fantastic if you can't decide on a particular film or theme for your party. It lets your guests decide who/what to dress up as, and show their personal taste and preference. Most people you invite will probably have a costume in the back of the wardrobe, or can put one together quickly, which makes it better for last minute parties!