Ok so I have an 02 Altima with the 3.5 and 120k on it. It has always run great, have had no issues and never leaked a drop of anything.

I changed the oil about 3 weeks ago in preparation of two long road trips, 2500 miles in the last two weekends. Now I get home 2 days ago and found it had leaked a fair bit (about two quarters sized) on the driveway for just a few minutes of parking. It appears to be dropping off the back of the passenger side control arm behind the oil filter.

I have not gotten under there fully yet but I am today. what do I need to check? I always double check the oil filter seals and tighten everything when I work on it. Anything thats prone to go out quikly like this? I am not a Nissan guy too much, more Jeeps so I need some advice here.

The oil filter screws onto the oil cooler. Sounds like you need the o-ring that is behind the oil cooler. Fairly common problem. About $8 for the o-ring. Just change it next time you change your oil.