Welcome to Gaia! ::

I would say

Clone skill (Bunshin no jutsu)

since his jutsu Dance of the Crescent moon (Mikazuki no mai)
is a sword technique which creates two clones that attack simultaneously to confuse the opponent.

in addition I would think:
Dispell (Kai)
Body substitute skill (Kawarimi no jutsu)*
Transformation skill (Henge no jutsu)

since they are pretty basic.

& possibly: Pain of a Thousand Years (Sennen Goroshi) Because he is quick with his finger as you see in the episode where he stops Neiji.

*his reason for not using that one is that he was caught of gaurd with nothing to switch with

wow so i was right! score! *victory dance*

I thought of one. (this is a made up one) Germ-Spredding no justu: Hayate builds up chakra in his lungs, then gets in the enemies face & has a really bad coughing fit. xd

Hayate: Germ-Spredding no jutsu! *cough*cough*hack*choke*cough*wheaze*cough*gasp*hack*wheaze*cough*

Baki: [cringes & whipes his face] ha.. is that all? That justu took more out of you then it did out of me...

Hayate: *gasp*pant* Maybe... but...

Baki: but nothing! Your jutsu had no effect!!

Hayate: ...give it a few years...

Baki: Whatever... [kills Hayate]

OMGTIMESKIP

Baki: Alright guys it's time to att- *hack*cough*cough* attack Konoha!! *cough*wheaze*

Kanekuro: uhh... are you feeling alright Baki?

Baki: no... actually... I- I feel like crap. (has a really bad coughing fit & dies)

Temari: do you think he was contagious?

Gaara: I don't know, but it's a possiblity...

Kanekuro: *coughs*

Gaara & Temari: stare

Kanekuro: why are you looking at me like that? sweatdrop Guys? eek Guys!?!

Gaara: Dessert Coffin! [crushes Kanekuro]

Temari: [blows bloody sand away with fan] um... Gaara-kun... do you think that was nessiarry?

Gaara: of course... he would have gotten us all sick...

Temari: um... yeah sweatdrop *swallows back a cough*

Hayate: (is watching from heaven & laughing)