In MY humble opinion.  Since Will Ferrell is my favorite actor, I felt compelled to make this list?
(These movies have Will in one of the "lead" roles...that means "Wedding Crashers" and "Austin Powers" don't count...)
How does it stack up to YOUR list???

5-TIE:Step Brothers / The Other Guys

4-Old School

Best Line: 

Marissa: [after seeing Frank running naked along the streets, she slows down her car] Frank, what are you doing? 
Frank: [out of breath] We're... We're going streaking! We're going up the quad and to the gymnasium. 
Marissa: Who is? 
Frank: Th... W... There's more coming. 
Marissa: Frank, get in the car. 
Frank: But... everybody's doing it. 
Marissa: Frank! Now! 
Frank: [still out of breath] Ok. 

3-Elf

Best Line: 

Buddy: You smell like beef and cheese, you don't smell like Santa. 

2-Talledega Nights

Best Line:

Jean Girard: But you have forced me to do this. You are now mocking me and making me look ridiculous. Just say, "I love crepes." 
Cal Naughton, Jr.: You know, just to put this in there, I had a whole mess of crepes this morning. They're just like pancakes, maybe even better. 
Ricky Bobby: Wait, are they the really thin pancakes? 
Cal Naughton, Jr.: Yeah. 
Jean Girard: Yes they are. They are the really thin pancakes. It's just a French word for them. 
Ricky Bobby: Oh, my god, I love those. 
Cal Naughton, Jr.: Put any syrups you want on them. I'm just saying, think about it. 
Ricky Bobby: They come with cheese sometimes? 
Jean Girard: Yes, of course, a fromage-crepe. 
Ricky Bobby: Well, why didn't someone yell that right-right away? 
Jean Girard: Do you know what's in the crepe suzette? 
Ricky Bobby: Oh, I love the crepe suzette. 
Jean Girard: With the sugar and lemon juice... 
Ricky Bobby: Yeah, the sugar and the lemon juice. Sure. 
Jean Girard: Grand Marnier. 
Ricky Bobby: I wo - I wish I could crawl into one of those right now. I'd eat my way out from the inside. 
  

1-Anchorman

Best Line: 

Ron Burgundy: I don't know how to put this but I'm kind of a big deal. 
Veronica Corningstone: Really. 
Ron Burgundy: People know me. 
Veronica Corningstone: Well, I'm very happy for you. 
Ron Burgundy: I'm very important. I have many leather-bound books and my apartment smells of rich mahogany. 

(The only other one that was VERY hard to leave off the list was the "The Lost Anchorman Movie" which was only available with a special DVD set sold in 2004/2005. Not many people have watched that tho.  I have - it's HIGHLY recommended.)

Just for reading this whole blog post, here's a treat:  The trailer for Anchorman 2!!