The best $10 I've spent on a set of games since X-wing vs. Tie Fighter!

 

Sid Meier's Ace Patrol (WWI free to try) $4.99 for all the campaigns after the first free trial.

Sid Meier's Ace Patrol: Pacific Skies (WWII Pacific) $4.99

 

It's similar to the board games but on your phone or tablet.

Cool, I'll have to check them out!

I've got the WWI game -- it's good fun!  I'm showing my age, but the mechanics remind me a bit of the old 'Ace of Aces' picture-book games where in each turn, you and your opponent would each choose a manoeuvre, read off page numbers to each other, and then turn to those pages to give a new cockpit view of the situation: http://maverick.brainiac.com/aoa/aoa1.html.  (There was no board, but there was a kind of hex-grid implied underneath this system.)

 

S!

 

Maus

I played Flight Leader by Avalon Hill when I was a kid and it's pretty much the same concept.  I like that there are a ton of different difficulty levels so the replay value will be decent.