Open windows maximized!

This can be done with CCSM's Window rules.

CompizConfig Settings Manager (CCSM) is available in Universe section of repository, so allow the repo. and install it using:

sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) universe"
sudo apt-get update
sudo apt-get install compizconfig-settings-manager

The Steps:

1. Start CCSM, and go to Window Management. Check mark Window Rules and click;

2. Under the Matches tab, click the + button next to the Maximized field so that Edit Match window appears;

3. In the Edit Match window, select the Type you want and use Or for the Relation. Next open the the target application which you want to start maximized each time it is called (in the example snapshot below I'm using Chromium browser as the new target; I've already added Software Centre to the rule). Then click the Grab button in Edit Match window so that a reticle or crosshair appears; move it over and click on the target application's window. The proper value should then appear in the Value field, and click Add;

4. That's it, you can add more applications to the rule or reset by clicking the reset button next to + icon.

Similarly you can set the rules for Fullscreen, Non Movable windows, etc.

You can also specify custom sizes for application window under Window Management -> Window Rules -> Size Rules.