Real hair's the best bails, but the monofibre ones can look quite decent these days.
Let a hairdresser put them in for you, and go for the plait and glue type of hold. I had half a head done some years back (a full head's too many), which'd supposedly last for 3 months. I had them in for 7, so felt it was worth the money.
If you just want them in for a special occasion, you can buy the clip-on ones, but if if it's windy and your hair blows about, you can see where they've been put in.