Puzzle time! Three puzzle games that are guaranteed to keep you busy for a very long time, mostly because they're fiendishly difficult and have hundreds of puzzles to complete.

Doodle God - The tantalizing Flash game is now on your iPhone! You start with just a few elements — air, water, fire, and earth — but must combine them to eventually form well over 100. Tap one category to open up its sub-types, tap another to bring it up on the other side of the screen, then tap two elements to see if they mix. If they do, you get a brand new element to play with. If they don't, you get nothing and must keep trying. It's a bit trial-and-error in nature, but superbly captivating all the same.

Trainyard - A blue train wants to leave the station and make it to the blue goal. There's no track, unfortunately, so it's your job to draw it. Now, what if a red train and a green train leave separate stations and want to reach the same goal? That'll require a bit more track, a few track switches, and a little thought. What about combining trains and trains that need to change color? That will require a lot more thought, a lot more track, and probably a few tricks you've never thought of before. An excellent puzzle game with loads of levels and a wonderful level of challenge. You'll never get tired of this one. Seriously.

Aqueduct - Another area that's ripe for puzzle exploration is water running through pipes. Aqueduct takes this to a simple new level by combining pipe tiles with a sliding puzzle of sorts, challenging you to not only move the right pipe pieces in the right place to let the water flow, but to move them without blocking each other's path. If you hate sliding puzzles like me, you won't have anything against Aqueduct, as it's pure puzzle awesomeness, plain and simple. And you gotta love that visual style!

NOTE: Games listed may not be available outside of North America. Prices are subject to change and are therefore unlisted. Please see the individual game pages for purchasing info.