I can't believe I only discovered this thread a couple of nights ago! Been meaning to add my own collection ever since.
I have: a LOT of Harry Potter sets. Lots of the buildings, moving models of Hedwig, Fawkes, Dragon and Buckbeak. Dobby, the Patronus, Ministry of Magic, Shrieking Shack, many more.
I also have the tuxedo cat (possibly my favourite to build, and I mistake him for my actual cat at least once a day), a couple of the small architecture sets (London and New York), the rainbow everyone is awesome set, and a Christmas tree. I've built the Piranha plant set with my son and helped both boys with various Mario/car/unicorn small projects. I also have quite a lot of Botanicals but I'm currently rebuilding them after they had run-ins with the cat and my 5yo. Oh, and I have a fab light-up cabinet full of Potter minifigs.
This morning I went to the Lego shop in Liverpool, armed with a gift card I was given when I left my job just before Christmas. It was lovely a quiet, and it's always so well stocked. I've been to a few of the shops but it's my favourite one. I spent ages dithering, but eventually treated myself to Concorde! I'm a big aviation geek too. Can't wait to get started. They had lots of the retro radio sets in stock, for those who were looking for it.