I love making chocolate mousse, cheesecake, or a similarly simple but decadent dessert, and once the kids are asleep have some with a glass of wine and a movie, or reading next to our (gas) fire. Another is to simmer dried apricots in water, sugar, and brandy, let them cool, then half-dip in melted dark chocolate. Real hot chocolate is great too - sugar, grated chocolate, cocoa powder, vanilla, and milk.
I have family hand-me-down Wedgwood and sterling flatware, so I'll do dinner for us using the good stuff. Put a nice tablecloth and candles on the table, and make it all special. We have a deep freeze and buy our beef by the side, so even good steaks average about $3.50/lb. I can do shrimp, steak, goat-cheese mashed potatoes, and a vegetable for <$10 for 2 people.
Pack a picnic and enjoy the day out. We used to go to our local botanical gardens all the time. They even had a kid's area with fountains to play in. It did cost for admission, but we became members and our averaged cost was $2/visit. The gardens had a weekly summer concert series included with admission. We also have a national parks pass (free for AD military), and so we make use of that now to go hiking and enjoy incredible views.
We also used to live right near the beach, and that was a great cheap thing to do. Sometimes we'd wait and go after dark to wander along in the edge of the water.
Hot bubble bath with a book.