We usually just come up with stuff ourselves, but newspapers and the internet are good sources for ideas if you are running dry on ideas. And friends and neighbors are always a good source of ideas, too, if you have similar interests.
Things we like to do as a family with our 12-year-old--bike rides, game night at home (board games or cards), movies (at home, at the local theater, at the drive-in), bowling (candlepin and "big ball bowling"), golf (mini or regular), swimming, camping, hiking, blueberry picking, Boy Scout outings, go to the library, go out to eat, read books (out loud to each other or all of us in one room with our own books), play outside (catch, batting, frisbee), play inside (with Legos, stuffed animals, Wii), letterboxing (goggle it), sit by the fireplace and listen to music, ice skating, sledding, cross-country skiing, vacations (train ride from coast to coast, drive from NH to Wyoming and back while reading a Harry Potter book from start to finish to each other and stopping for all sorts of interesting sights), Museum of Science trips, meteor shower parties, going to bed at the same time in the same room on occasion and pondering life's questions, etc.
When he was younger, we used to have Fabulous Friday Dance Parties in our living room. The three of us would put on a bunch of fun music and dance our hearts out. But currently that is "not cool". Some day we'll be able to do that together again, right?! : )
When he was younger, we would also do kite flying, painting, drawing, walks, the playground, cleaning (ah, those were the days when that was still fun!), tinkering on the piano, puzzles, puppet shows of our own, plays, air guitar, drumming (on pots and pans, or whatever made a sound), swinging, climbing, tumbling, laying on the ground looking at clouds, stargazing, planting, storytelling, singing, building snow men/snow whales/snow forts, having snowball fights, making snow angels in our yard or in the neighborhood, catching snowflakes on your tongue....
Some of those things we still do, but kids' interests change as time goes on. The trick is to have unplugged time together--no earbuds, no screens--just you and your kid(s). The gift of time is the important thing...at any age. The sky is the limit!