Thanks for the suggestions Aly. I thought they were worthy of an update blog entry. I've copied the comments below.
I've been to Amsterdam and loved it. I'll certainly have to take Mick there (Holland is half my family heritage). We will have to choose the right time to visit the Keukenhof. What a sight that was! I'll also have to make sure he sees Helsinki in Finland (the other half of my family heritage).
And, a personal "must see" are the Northen Lights. I've watched the Joanna Lumley DVD of her journey to see the Northern Lights about 5 times. I'd love to see Tromso and where the Samis live, and also Rovaniemi in Finland (who wouldn't want to visit Father Christmas!)
Bruges is also well worth a visit. I've been there very briefly once but would like more time to look around. Vienna is a great suggestion too - and somewhere I've never been. Plus... I'd like to do a train trip through the Swiss Alps.
Scotland is definitely on the agenda and also Ireland, but these would be by car rather than flying there.
So here's a list that we'll be able to choose from when looking for cheap flights!