Here are my entries :
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Tele-gravi-spectro-scope©®™_
An utility module that would allow you zoom in (via a PiP sort of window covering middle part of the UI) and also get "real" image of targeted body instead of a default hologram (provided the body is in the operating arc of the utility slot). Additionally it would allow to set destination to any star you see from your cockpit and display star-type and total mass of selected star system (the mass part is kind of a irrelevant, but it is a part of an idea I had on how to make exploring unknown systems more interesting... alas that's not what this thread is about

)
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Modular limpet-controller_
Would have X number of sub-modules that can be filled (sort of like you equip SRVs and SLFs), which decide the type of limpets it controls. Allows having multiple (up to 3 for the largest?) controllers in one slot, with a downside of perhaps being larger than those controllers combined and that the changing sub-modules requires being docked. Would greatly cut down the insane amount of control modules we have; perhaps a single sub-slot version (with the same size as the current ones) could even replace them altogether.
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External pylons / Utility-module-PDT-conversion_
For small-sized vessels -- basically an armour modification that adds a number of external weapon pylons (sort of like a lot of modern aircraft have) that can be equipped with some normal small weapons, but with i.e. reduced ammo capacity (so, like two missiles or a gimballed-only MC). Has impact on hull hitpoints but allows for more firepower/versatility.
For large and perhaps medium vessels -- allows installing a turreted MC into utility slot, to serve as point-defence weapon against fighters, small vessels, and even missiles (though with higher power-draw and less effectiveness than a dedicated PDT)... this one is, I think, just because I've watched a bit too much of WoWarships recently and a lot of AA-style tracers spewing from a space-ship would look rather awesome!

The pylons/converted-util-slots could also serve as slots for less combat-oriented stuff (like additional headlights mentioned in previous posts).
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Ship-to-ship docking umbilical_
Might not even need to be a separate module, just a function of our multi-purpose cargo bay door, really, and (in the fantasy future game) would allow face to face meetings, crew/passenger transfers, repair crew access and raiding ships/stealing cargo "manually".
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Ram-spikes external module_
Sort of an actual working (even if a bit insane/impractical/quite-probably-nonsensical) implementation of the "raider" skins, which upon ramming another vessel fuses the two together, until one of them is destroyed (you would still be able to fire weapons) or the spikes break (due to continuous conflicting thrust vectors). This one is an absolute "what-if" fantasy module, that probably doesn't really fit Elite in any way, but the image of two ships thrashing around, trying to ram the other into an asteroid, while their guns fire continuously seems pretty darn awesome in my mind!
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Ejectable power-plant core_
Either a modification of the PP or a standard function, that allows for (manual only) removing of the core, to prevent explosion. Can only be replaced by 3rd party... (...because, seriously, we all watched Star Trek, and always wanted to be able to do that!).
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Escape pods_
Should really be a standard module. All I'm saying on the topic...
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Planet surface de-beige-ifier_
Okay, I'm just being flippant right now... [noob]