Astro Boy is by Treasure, the same people that brought the gaming world Gunstar Heroes for the Genesis, which, by chance, is getting a GBA sequal in the form of Gunstar
Super Heroes. It comes out this month, if you wanna wait for it.
Kingdom Hearts: Chain of Memories is good, too, although I think that, save for a quick save feature, it plays out more like a console game. Still magnificent though, with good replay value.
If you can track it down, I'd also suggest Super Dodgeball Advance -- if you've played the Neo Geo dodgeball games, you'll know what to expect. I saw a used copy at a Game Crazy near me for about twelve bucks, if you want a price range.
Bubble Bobble Old & New -- scweetums. (In the form of a classic arcade hit)
Megaman Zero is pretty much a safe bet, although it is MINDNUMBINGLY hard at times.
Wario World 4 is also very fun, but it was a launch title, so I don't know what your odds of finding a copy today are.
Fire Emblem: The Sacred Stones is also a great strategy game, since I see you have Advance Wars and Tactics Ogre on your list.
Lastly, there's Advance Guardian Heroes from our good friends Treasure -- I've heard people say that it's only a shadow of what the Saturn version was, but since I don't have money coming out of my ass, I've never owned or even played it. What I can say though is that it is a fun GBA game.
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