As you probably noticed, in 0.95 starting forces are essentially the same pairs of Lancers and Carracks everywhere you go. In 1.0 and on, the galaxy will be far more populated when you start off a game.
Most prominently in a post Imperial-collapse galaxy, are the various Warlord groups. In the areas of space canonically controlled by these independent Warlords, you'll find their forces on patrol, with a bit of different composition depending on the group in question. Their canonical capitals also act as strongholds for their mini-Empires, where you'll find the Warlords themselves leading their fleet from their own flagship, such as Zsinj on the Iron Fist (see below). These Warlords were often quite fond of Super Star Destroyers, so their fleets can put up a fight against even the strongest of your forces. For those more familiar with the lore, along with Zsinj's empire you'll find Greater Maldrood, the Eriadu Authority and Zero Command.
In the non-Imperial parts of the galaxy, you'll also be able to find appropriate forces defending their planets with their own unique ships. Chief among these are the Ssi-Ruuvi and Hapans. How far we take this depends mostly on the limitations of Sins, since we're prioritizing stability over having more militia.