Cost: 1. XP: 2.

Choose a card in your play area or reveal a card in your hand. Search your deck for another copy of that card and draw it. Shuffle your deck.

"... all life is only a set of pictures in the brain, among which there is no difference betwixt those born of real things and those born of inward dreamings..." - H. P. Lovecraft, "The Silver Key"
Romana Kendelic
Dark Side of the Moon #205.
Lucid Dreaming

For everyone's benefit, here is a list of the cards that most obviously synergies with Lucid Dreaming (as of Dream Eaters). Please mention any that I miss out in the comments:

Signature Cards:

Stack-able Hand Assets:

Disposable/Temporary Assets With Persistent Effects:

Most of the Myriad Cards:

Cards That Synergies With Themselves:

And that should about be it. Of course Lucid Dreaming has additional functionality outside of these cards; drawing the second copy of your 5xp sink or your assets with limited uses is always a good thing. And of course, not all of the cards presented are particularly powerful with Lucid Dreaming (e.g. Knife); this list it just a time saver for everyone who wants to know where Lucid Dreaming goes above and beyond a card draw.

Lucaxiom · 1553
a) Yes you can trigger two copies of Survival Knife on the same attack as they are responses on two different cards. b) why would Hot Streak 4 and Expose Weakness 3 not make the list? — slothgodfather · 7
Expose Weakness (3) reduces the fight value of an enemy to zero. A second Expose Weakness (3) would also reduce the fight value to zero, AKA make no change at all. As for Hot Streak (4), I'll admit my reasoning is quite tenuous; essentially, you won't really need one copy of Hot Streak (4) to trigger another copy, as the cost of 3 resources is affordable. Hot Streak (2)'s 5 resource cost will generally need assistance from another economy card; it doesn't have to be another copy of itself, but it can be, and thus is included on this list — Lucaxiom · 1553
I think it's also quite good for various Talent Assets which you are allowed to have 2 copies of in play. I was thinking cards like Pathfinder, Fieldwork, Drawing Thin, High Roller, Pickpocketing, Well Prepared, etc. Whether it's really worth 2XP, and 1 Action/Card/Resource just to draw the 2nd copy remains to be seen. — Faranim · 245
In anyone with seeker card access, the full-deck-search means a guaranteed Astounding Revelation trigger (or Occult Evidence, if you're Mandy), which is significant value. And of course, Mandy can run this to grab the 2nd & 3rd copies of Segment of Onyx with her special ability, which is pretty rad. — NatesPromNight · 445
It also guarantees a Shocking Discovery trigger for Mandy, if she hasn't dealt with that yet. — CSerpent · 76
You missed out Dream-Enhancing Serum, which will draw you a second card as you reveal both because Lucid Dream specifies its a card draw to which you can react. — The_Wall · 172
Your discard pile is also in your play area. — Dis · 1
@Dis: Nope. Discard piles are specifically out-of-play areas, which are contrasted to players' play areas, which are (logically enough) in-play areas. See "In Play and Out of Play" (and "Discard Piles") in the Rules Reference. — Tamsk · 1
I'm not a huge fan of Empower Self, really. But at least you can find the other versions with one of them in hand/play and Lucid Dreaming. Although it's making a slow, expensive and clunky card even slower, more expensive and more clunky. — olahren · 572