The Clone Wars - S2E12 - "The Mandalore Plot"

12:08 - Obi-Wan:  "I am here on a diplomatic mission."  The phrase "diplomatic mission" occurs a couple times in A New Hope.  Captain Antilles tells Vader that "We're on a diplomatic mission" [5:55], and later Leia tells him, "I'm a member of the Imperial Senate on a diplomatic mission to Alderaan" [7:58].

20:33 - Pre Vizsla:  "We'll catch up with the duchess soon enough."  Perhaps coincidentally, Tarkin has a similar line in A New Hope when he tells Leia:  "We will deal with your Rebel friends soon enough" [58:45].

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As Dave Filoni explains in the featurette for this episode on the Star Wars website, the painting in Pre Vizsla's meeting room (first seen at 10:55) is in the style of Picasso's Guernica.

The Clone Wars - S2E11 - "Lightsaber Lost"

1:58 - Ahsoka:  "I, I was checking out a suspect.  I had a bad feeling about him."

2:44 - Ahsoka:  "He [Anakin] tells me over and over, 'Your lightsaber is your life; don't lose it.'"  In Attack of the Clones, Obi-Wan tells Anakin, "This weapon is your life" [21:59].

2:51 - A file in the Jedi library shows a woman who later appears in the cantina in A New Hope [first in a wide shot at 45:04, then in a closer shot at 45:40].  According to the trivia for this episode on the Star Wars website, this is Brea Tonnika.

[source]

21:17 - Master Sinube (to Ahsoka):  "Pass on what you have learned."  Yoda also says this (to Luke) in Return of the Jedi [44:11].

21:45 - Ahsoka (to a group of younglings):  "This weapon is your life, but it is also your responsibility.   Don't let it out of your sight."  An-other reference to Obi-Wan's "This weapon is your life" in Attack of the Clones.

The Clone Wars - S2E10 - "The Deserter"

13:51 - Battle droid (to General Grievous):  "Roger, roger, but I must inform you, sir, there are multiple life forms approaching from the east and west."  This is somewhat similar to C-3PO's "There are several creatures approaching from the southeast" in A New Hope [28:31].

15:48 - Clone trooper (to an-other clone trooper):  "Great shot!"  There's probably not much of a parallel to be drawn, but Han Solo says something similar to Luke at the end of A New Hope:  "Great shot, kid!  That was one in a million!"  [1:57:20].

The Clone Wars - S2E9 - "Grievous Intrigue"

4:23 - Plo Koon:  "Commander Wolffe has found a message in the holo-transmission.  Play back the message."  This bears some resemblance to what Luke says to R2-D2 in A New Hope:  "Play back the entire message!" [22:59]

11:15 - General Grievous:  "So, Kenobi, is everything going as planned?"

Obi-Wan:  "That depends on your point of view, General."

This seems to be a reference to Obi-Wan's "from a certain point of view" in Return of the Jedi [46:23].