I cannot believe that more people havent posted some here...
There are TONS of Veronica Mars Fanfics at LJ Here are just two of the many comms.
VeronicaMarsFanfic
Here is a good
VeronicaLogan
A couple of my favorite arthors are Sadie_Katie and Sexyceral they are awesome, but there are countless communities with hundreds of fan fics. I live there and in Neptune_Video.