Go up in a glider. I've always loved flying as long as it's not in a commercial plane (I do hate all the messing about at airports) but have never been up in a glider, although I've been up in a hot air balloon. There's something very peaceful about being up in the air.
Visit Iceland. It's always been ruled off our holiday list as being too expensive, but since my sister-in-law went a few years ago I've wanted to go. I'd love to see the Northern Lights.
Dinner on the Orient Express. This one is potentially easier as voucher companies have this all the time. It's only the getting there that has put me off. I love Agatha Christie, so the idea of going on the Orient Express - even within the UK - thrills me.
Write for Harlequin. I've looked into this one more since they started their Dare line, but so far have been put off by the long list of requirements. However, I may get there in the end.
So what's on your list?