Sometimes we forget that our Android phones are, well, phones. For those times when you need to make a call, it's handy to have a speed dial list. And it's easy to make one. Open your dialer, some phones have a dedicated button, some have a shortcut icon on the desktop, and all have a phone app in the applications tray. Once you get it open, hit the menu button and look for the Speed dial button in the lower left (number 1 above). Give it a tap, and a new window will pop open (number 2 above) and you just hit the Add new button. After you pick a contact, you get to assign it to any available number on the list.
Note that this may vary by phone. It's in Sense, and on the Captivate and Vibrant, as well as the Droid X. Stock Android? Not so much.
Pro tip: For those numbers that you find yourself always calling, you can add a direct dial icon to your homescreen by long pressing an available 1x1 spot, and choose Shortcut > Direct Dial from the menu. And don't forget about voice dialing!