13. Michael Cera

Character: Cera had a bit part in season 3 as peppy Hearst College orientation guide (and exposition dialogue deliverer) Dean, who partners with Veronica during an icebreaker because no one else would. (Aww.) He was memorable enough for producers to ask him back in the third season, but a scheduling conflict kept him from a repeat performance.

Episode: Season 2, Ep. 16: "The Rapes of Graff"

12. Alyson Hannigan

Character: Hannigan played Logan's attention-seeking sister Trina, who often covered up her tortured soul (distant parents, abusive boyfriends, etc.) with a smile and a witty barb aimed at Logan. Trina's lack of empathy for Lynn's disappearance (she used her possibly dead stepmother's credit card, after all) caused Logan to break down after he and Veronica attempt to track Lynn down.

Episodes: Season 1, Ep. 15: "Ruskie Business"; Season 1, Ep. 19: "Hot Dogs"; Season 2, Ep. 9: "My Mother, The Fiend"

11. Jonathan Taylor Thomas

Character: Jonathan Taylor Thomas certainly enjoyed his turn as the villainous Ben on Mars after all those years on Home Improvement. Ben was the definition of Neptune, as a corrupt ATF agent in the sheriff's department who tried to frame Norris Clayton for bomb threats at Neptune. Veronica and Logan's takedown of him and his plan — along with their subsequent makeout sesh — remains one of the most memorable cases handled by Mars Investigations.

Episode: Season 1, Ep. 18: "Weapons of Class Destruction"

10. Adam Scott

Character: Scott's likability was used effectively during his stint on Mars. As Veronica's favorite teacher Chuck Rooks, he engaged his students better than anyone else at Neptune High. And by engaged, we mean he had an affair with a student, leading said student's best friend Carrie Bishop (Leighton Meester) to exact revenge. It's an episode in which Veronica's judgment gets clouded by her affection for Mr. Rooks, and has to reconcile his ugly secret with the personable history teacher she had admired.

Episode: Season 1, Ep. 14: "Mars vs. Mars"

9. Paul Rudd

Character: Of course Paul Rudd is memorable. The actor played Desmond Fellows, a washed up singer of a popular '90s band called My Pretty Pony, who arrives at Hearst to perform a benefit concert. His backup vocal tapes go missing, so Piz (Chris Lowell) recruits Veronica for help, despite Fellows' sleazebag ways.

Episode: Season 3, Ep. 17: "Debasement Tapes"

8. Jessy Schram

Character: Schram's Hannah is high on this ranking not because of star power (though her Bonnie Whiteside on Mad Men is fabulous), but because Hannah was a notable season 2 guest star who changed the course of Veronica and Logan's relationship. But she wasn't just the catalyst for this epic scene — she also stood her own as a character, and was memorable for Logan's betrayal of their relationship, so much so that fans put together elaborate videos dedicated to them (see below).

Episode: Season 2, Ep. 13: "Ain't No Magic Mountain High Enough"; Season 2, Ep. 14: "Versatile Toppings"; Season 2, Ep. 15: "The Quick and the Wed"; Season 2, Ep. 16: "The Rapes of Graff"

7. Charisma Carpenter

Character: Kendall Casablancas is a toss up, to be honest — you either loved her conniving ways, or you hated her for destroying the lives of Dick, Beaver, and Logan. We love her. She never tried to cover up the fact that she was a gold-digging trophy wife to Dick and Beaver's real estate magnate father, and she was never all that into hiding her affair with Logan. Best of all, she made a hell of a morally gray villain and banter partner for Veronica.

Episodes: 10 in season 2, 1 in season 3

6. Leighton Meester

Character: Why is Meester ranked higher than, say, Paul Rudd and Adam Scott, you ask? Because Carrie Bishop was integral to Veronica's character — and was arguably the most memorable guest 09er with the fewest appearances. As the gossip queen of Neptune High years before Gossip Girl changed the course of her career, Meester relished torturing Veronica for being different from the 09ers, though she later developed a shaky alliance with Veronica during the Chuck Rooks case and helped Veronica figure out who raped her at Shelly Pomroy's party.

Episodes: Season 1, Ep. 14: "Mars vs. Mars"; Season 1, Ep. 21: "A Trip to the Dentist"

5. Ken Marino

Character: Vinnie Van Lowe was hilariously frustrating. There's nothing Vinnie wouldn't do to get the best deal out of his client (including dropping them, a move he dubbed "The Vinnie Classic") and to mess with Mars Investigations. Then again, he did help Duncan escape and has rescued Veronica from sticky situations. And Ken Marino? Perfect casting for the guy, as evidenced by the clip below.

Episodes: 10 through three seasons

4. Harry Hamlin

Character: Hamlin played Aaron Echolls, Logan's father and the stealth Big Bad of season 1 who would return again and again as a thorn in Veronica's side. Aaron, an action film star, often appeared in public as a typical Hollywood actor and loving father. In private, he was abusive and — spoiler alert except why you would be reading this if you've never watched Veronica Mars is a mystery — Lilly Kane's murderer, making him the man who indirectly changed Veronica into a gumshoe.

Episodes: 12 episodes through seasons 1 and 2

3. Krysten Ritter

Character: Gia Goodman was one of kind — she could confuse chlamydia for a flower, psychoanalyze Logan during party chit chat, and partake in the coverup of a murder that would haunt her post-Neptune. Nothing says 09er like Krysten Ritter's character; Ritter herself, meanwhile, has also shot to success following her turn on Mars, most notably as the titular B in Apartment 23.

Episodes: 8 through seasons 2 and 3

2. Max Greenfield

Character: Before he became the womanizing Schmidt on New Girl, Greenfield played the honorable, lovable, and adorable Sheriff's Deputy Leo D'Amato, who both dates Veronica and helps her track down the necessary documents for her "hobby." He left enough of an impression for fans in season 1 that he ended up returning for a total of 11 episodes throughout the series (and a welcome appearance in the film), charming Veronica as the Nice Guy before Piz ever showed up. (And don't get us wrong, we love Piz. Leo just holds a special place in our hearts.)

Episodes: 11 through three seasons

1. Amanda Seyfried

Character: Seyfried aced all categories as Veronica's best friend Lilly Kane, whose murder set the series in motion. She only appeared in flashbacks, home videos, and dream sequences — some sweet, some sad, some terrifying — but she always left an impression, both on Veronica's character and on audiences. Lilly's murder, though resolved by the end of the first season, left deep scars on every major character in the first two seasons — so much so that by season 3, when Lilly didn't appear, fans felt eerily abandoned.

Episodes: 11 through seasons 1 and 2

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