You mean for example Wit's End and Madred's Razor? Yup.
I think the only exception is Wriggle's Lantern and Madred's Razor who don't stack even though they are two different items.

I thought the rule on Unique Passives was that if it was built in the same line, it wouldn't stack. For instance cooldown reduction on item combos like Brutalizer/Yuumu's Ghostblade, Fiendish Codex/Deathfire Grasp, Codex/Nashor's Tooth, and Glacial Shroud/Frozen Heart. Also, I didn't think Sheen Stacked with Trinity Force/Lich Bane, and fairly sure Trinity Force doesn't stack with Lich bane as well. And the last I can think of at the moment is Tear of the Goddess/Archangel's Staff. I could be wrong on some of those, but I'm fairly certain on most.

i was disappointed when I found out rylai's don't stack even thought its not a unique passive.

Slows don't stack, that's why Rylai's does not. The stronger slow will take over.