In many ways, choosing the right outfit for a big occasion can be tougher than choosing one for everyday: after all, it's important to strike the right balance between smart and not being overdressed (unless, of course, the event is a major one). A formal dress and jacket is often a great way to go, and can definitely be stylish when done right.
For some people, a formal dress and jacket will mean a more professional outfit, where as others might wear it during a night out on the town. This is entirely a matter of personal preference.Another key consideration is the colour. Those seeking to go for that more professional combination should focus on darker colours (though there's still something to be said for a cream suit), whereas those who are on big night out usually have more options to explore.
As with all forms of clothing, it's a very good idea to go second-hand - especially if you are looking for a smart outfit, as this will often be half the price of a new one, and will probably only be worn once or twice.