I have three – note, all pics copyright other people.

Though it's not a real castle, i spent a lot of time playing there as a child when we went to visit family – Castell Coch, Wales:

I spent a beautiful day on the beach last September. Another folly – Dunstanburgh, Northumberland:

Hugely impressive, and somewhere I'd like to visit again. The Red Fort, Agra, India:

Orford Castle was local to me as a kid and I rather like it still

Oh, yes, I nearly forgot this place, which was but a few miles away from where I grew up – Broughton Castle:

Bamburgh castle is a bit of a con really. the actual real castle is quite small, although very important to the history of the UK. Lord Armstrong acquired it in the 18th century and added pretty much all of the buildingswe see today. Still a beautiful sight though.
I love dunstanburgh too, the walk up to it is great, especially on a cold windy winters day!

Llanstephan Castle

On a more serious note I always quite liked Kilkenny Castle, nice playground.

Another vote for Dunstanburgh Castle, Northumberland. Stunning sight on the wild coastline.

Dunstanburgh:

I'd better say Dundas Castle, seeing as I'm getting married there in a couple of months…

I've also always like the look of raby castle, but never has a good explore of it

Tattershall castle, Nottinghamshire

Fond childhood memories

Tantallon

Also, used to live near Dunottar

And last, but far from least, Kisimul

Going slightly off topic

When God decided the world was a big mistake and was going to wipe it out and start again, he instructed Noah to build an Ark. Howebver, he was on especially good terms with McNeil of Barra, the inhabitant of Kisimul castle and asked if he would like a place on the Ark
"Och no you're fiine" replied McNeil "I have a perfectly good boat of my own"

Thanks Rusty! Ahh, wish I was there….

Castle Drogo. It may be a modern impersonation, but I like it.

I like that one (points out of window into darkest Conwy)

Not really a castle but I always thought these were impressive:

Solent Sea Forts