GameMaker - Free for Mac/windows Export, $9rt9-$800 for other Exports - Easy to set up and use. Requires learning GML (Game Maker Language) which is fairly easy to learn and very efficient. Has a Large supportive community backing it. Recommended for 2D games, but has capability for 3D built in.
Construct 2 - $130 personal license, $430 business license - Similair to Gamemaker uses a standard codebase for exporting to multiple platfroms. Recommended for 2D games.
Unity - $1500 or $75/month + $1500 or $75/month for iphone/android Exports - Extremely powerful development suite. Has a high learning curve yet extremely functional. Recommended for larger games and 3D games.
OpenClipArt - Free graphics, very useful in creating sprites for games
OpenGameArt - Huge databse of art specifically designed for gaming. Ussually the first stop for finding what I need
DeviantArt - Sometimes free art just doesnt cut it. Go here to hire artists or buy their work