[Keeper of Dol Guldur]

The Elven rings heal and maintain things.

Rivendell, Lothlorien, Theoden and the spirits of every member of the Fellowship and soldiers of Rohan and Gondor are examples of their healing virtue.

They could also be used for concealing things from evil. Rivendell's location was secret to Sauron's wandering eye. Lorien was right under the nose of the tower of Dol Guldur, and nobody ever seemed to know what Gandalf was up to. His movements were secret, he was veiled from sight by a grey mist, as Celeborn the far seeing mentioned.

I think the only people who knew what he was up to were the other elven ringbearers ... and only if he wanted them to know.

Even the Nazgul couldn't detect the elven ring power until they were on top of it. They didn't know where Rivendell was until they were practically on its doorstep, three of them resided in Dol Guldur and had no idea about Caras Galadhon's power.

Oh yeah ... and Elrond's ring is probably what gave him power over the River Loudwater.

The Dwarven Rings were used in the discovery of precious metals. So, maybe the gems lit up when they approached lodes and veins of gold, silver and mithril. Something akin to that, possibly. It could have just granted some keen mining intuition.

The Nine rendered their wearers invisible, just like the One Ring. Of course, it seems like Sauron tweaked the invisibility spell into a 'permanently invisible and endless life, hahaha, you are my wraith now' spell.