I've read two really awesome Mentalist fanfics recently, both are AU after the season 3 finale, and they made me want more AU's in this fandom. My cravings are leaning a bit more towards the extreme AU rather than one that simply veers off course from current canon.
Mentalist, Jane/Lisbon- Post-apocalyptic world AU. I really, really want this.
Mentalist, Jane/Lisbon- Tossed into the wilderness AU. Along the lines of the X-files fanfic
"The Lost" by Wintersong, which I love to pieces. Maybe it's cliched, but I don't care.
The two Mentalist fics I read were:
The Red and the Grey by bloodwrites- Well writtien, awesome character portrayal, angst galore, and a wonderfully crafted plot.
a Road lEss TreveleD by 221b Baker Street- Is Jane psychic, or just insane? Awesome story with fantastic dialogue, and a plot that keeps you guessing.