These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: The Uhlek in the first game. Always hostile, and packing far more firepower than you could possibly carry on your ship. The Umanu in the second game are as strong as the Uhlek, but you can upgrade yourself until you're strong enough to destroy them, and unless you go poking around the nebula early, you won't see them until the end of the game.
Good Bad Bugs: The Amiga port of Starflight 1 has an underflow bug when selling items that gives you enough money to afford pretty much everything.