Well, I have several titles that I cherish because of the authors autographs and drawings, but I have to say my favorite is still the first - Croatian edition of "The Killing Joke", signed by Brian Bolland.
As for the most expensive, I think the title goes to the Croatian Absolute edition of the "Outlaw Nation" (which is also signed by both Goran Sudzuka and Jamie Delano, but it cost like hell).
In America, I didn't get too many signatures or drawings... I only caught up with Grant Morrison in San Francisco and got an autograph in the Comic Con catalog... And Terry Moore signed a TPB of "SiP" for me, drawings were to expensive... Oh yeah, Jimmie Robinson was promoting the first issue of Bomb Queen, so I can say I got the first issue and an autograph from an author no one knew anything about yet. 🙂