theory11 — Magic Tricks & the World's Finest Playing Cards

Any cool mentalism effects... ?

Yes there are.

...

Okay, smart ass response aside.

For PK, I can immediately think of 'Spin' by Matt Sconce. Completely impromptu, totally ungimmicked.

There's the DVDs 'Unexpected' by Marc Spelmann and Peter Nardi. That's all impromptu mentalism.

There's cold reading stuff.

Depending on how loose your definition of 'impromptu' is, there's nailwriter stuff.

Basically, start reading mentalism books and you'll figure stuff out. Fundamentals, Practical Mental Magic, 13 Steps, etc. Build up a base of skills and work from there.
 
Banachek's Pshycological Subtelties might be a good book for you.

(I'm assuming you already have 13 steps and Fundamentals. If you don't, why are you even asking?)
 
Are you looking for single tricks that you can crowbar into a card act to make it look like you're not a one trick pony or do you actually want to learn mentalism?
 
13 Steps has a few Mentalist card effect and so does the 39 steps and PMM.

In my opinion, there are very few good mentalist card effects. A mentalism effects is entirely different from magic. In magic, people typically associate that with "fast hands". Mentalism should come off as "body reading" or the real deal, or however you present it. Doing mentalism with cards makes you look like a magician, so all of a sudden you're just a guy showing tricks and puzzles, nothing emotionally investing. Cards just have a too strong connection to magic, and when I do mentalism, the last thing I want to seem like is a magician.
 
Called your bluff. The 39 Steps appendix contains no actual tricks. It's a bibliography. Are you sure you're not thinking of Fundamentals proper?