My guy (3yr old) loves perfection and operation (without batteries or timer) at the table by himself. Of course I put it away when he's not using it. Perfection has lasted a long time and has been much loved and used often as far as toys go. Just bought him magnetic Supermind and Mighty - too soon to tell, but I believe these too will have staying power as entertain yourself games.
Clue, monopoly, yahtzee, go fish, and connect four are fun, but those are fun because they're time spent playing games with momma. Side effect of yahtzee- the other day ds took a stray d6 from my jewelry box (souvenir of mine) and was rolling on the floor off the fridge and calling the numbers outloud. When I noticed he showed me the dice to prove he called the right number.
Since you have two kids already you could go with hungry hippos.
