Looking for ideas for specialized mounts, eh?
How about these:
Efficient Engine Mount - Reduces size and fuel consumption of engines, but increases their cost. Usable on scouts and cruisers.
Sniper Gunnery Mount - Increases range and accuracy of direct fire weapons, but also greatly increases their cost and size. Works best if weapons have a "blind spot" where they can't fire at ranges below, say, 10km - then the sniper mount would extend that blind spot as well as the max range of the weapon! Could work with any ship size.
Bombardment Missile Mount - Increases range and damage of missiles. (According to Devnullicus, this will actually work properly in SE5!) Increases size and cost. Usable on destroyers and dreadnoughts.
Carronade Gunnery Mount - Decreases range of direct fire weapons but increases their damage. Usable on frigates and battleships.
Reinforced Armor Mount - Significantly increases HP of armor and increases cost somewhat. Usable on baseships.
Miniaturized Electronics Mount - Reduces tonnage of electronics (sensors, scanners, ECM, cloaking devices, master computers, etc.) but greatly reduces their HP. Usable on scouts, frigates, and cruisers. Works best if these components are designed to be too big to fit reasonably on smaller hulls (say, anything smaller than a cruiser) - then cruisers become REALLY good at electronic warfare while destroyers, with their bombardment mounts, become the heavy hitters until you reach battleships and above!
Bulk Quarters Mount - Greatly decreases the cost of crew quarters and life support, but increases their size. Usable on colony ships, freighters, carriers, and worldships.
Planetoid Reactor Mount - Greatly decreases the cost of quantum reactors, but increases their size. Usable on worldships. Works best if quantum reactors are too bulky for all but the largest ships. Usable on worldships.
Hyper Beam Mount - Greatly increases the size and cost of beam weapons, but phenomenally increases their damage and increases their range as well. Decreases accuracy. Usable on baseships (even if there's only room for one beam per ship!) and worldships - think Death Star laser!
Oh, and by the way, if you can't increase the shield generation of shield generators with a mount, you can always reduce their tonnage and/or cost!
Ooh, and what if there were mounts only available through certain racial/unique techs? Like a High Energy Focus beam weapon mount available only through Crystallurgy?