If you're talking about AI, 3-4 hangars, 3-4 repair bays, and the rest beam turrets.  Fill the hangars with fighters. Put your beam turrets in front, with the repair bays and hangars farther back so they don't get primaried by everything.

If you've got Entrenchment, make sure to research the hangars' shield ability that gives everything around it 750 shields, and the Synergy tech for turrets which also gives them shields and a damage boost for each nearby turret (up to +1000 shields and 50% damage). Then throw in a Transcendia, close enough to the front but surrounded by the beam turrets and research its Meteor Storm and Mass Disorient abilities, and the AI will have a very hard time breaking it.

I play the TEC pretty much exclusively, so I'll just tell what I use for them. 

I usually have two mutually supporting repair stations, 5-7 hangars, and fill the rest in with Gauss turrets.  All of these structures support at least 3 or 4 of their fellows.  If you play entrenchment (if you haven't yet it is totally worth the $10) starbases are a deffinite must for planet defense.  At least with the TEC there is an upgrade option (I think it's called auxillary government) that prevents the planet from being conquered while the starbase is still present.  Also you can upgrade the TEC starbase to hold up to 14 strike craft squadrons.  Entrenchment also has alot of upgrades for the Gauss turret, makeing it very powerful for its size and cost.  Entrenchment can also upgrade the TEC hangars to be anti fighter platforms, though if there aren't any fighters in range they will attack any enemy ship in range.  As for strike craft mix, I split it pretty evenly between fighters and bombers.  I find the bombers are great against heavy cruisers.

A defence like this can easily stand off an AI assault with a 400 fleet cedit fleet without any entervention by a friendly fleet.