Similar in appearance and a few meters taller than the Eiffel Tower, Tokyo Tower stands at 333m, with observation decks at 150m and 250m which you can reach by elevator or via a long climb up the exterior staircase.
Dusk or early evening is the best time to visit, and regular musical events are held Wednesday through Friday evenings on the lower observation deck in a stage area called Club 333. Wednesday and Thursday nights are devoted to live performances of jazz and R&B, and Friday is DJ night from around 7-9pm.
Other attractions in the tower include a regular wax museum and a "Space Wax" museum (separate admisson), and some interesting historical exhibits on the third floor (free admission). Plus many, many souvenir shops, some notably less tacky than others.
There's a well-equipped play area for small children on the fourth floor, and if you're hungry, a good curry shop on the second floor called Tokyo Curry Lab.