I just found some more spoilers for the last couple of Veronica Mars episodes. They are just tidbits, I don't have any other information to go with them. As always, read at your own risk.
1. Aaron Echolls is found not guilty at his trial.
2. Weevil is arrested at graduation for Thumper's murder.
3. Mac and Beaver end up together again. It appears they finally move past first base.
4. Veronica graduates salutorian (2nd place).
5. Mac, Wallace and Logan graduate as well. Dick does not graduate.
6. Veronica dreams about what graduation day would have been like if Lilly were still alive. Lilly appears and this may be where Duncan's last appearance will be. In Veronica's dream she is with Logan.
7. Lianne Mars will also be back for the finale but it is unknown if she will be in the flesh or just in Veronica's dream.
8. Someone gets shot and it may be either Veronica, Keith or Logan. That person is NOT likely to die.
9. The final scene of the season is set at an airport. Possibly involving Veronica and Wallace.
10. Deputy Leo will be back for episode #20.
11. Clearance Weidman will be seen in the finale, possibly to related to Duncan's whereabouts.
Updated 4.19.06, 4.20.06, 4.21.06