This is a HUGE discussion on all forums. If folks were in a room, and not seperated by using these forums, fights to the death would be common.:matchup:
A coupla points people usually agree on:

1) change the oil regularly (3k-5k).
2) Use manufacturers recommended viscosity
2) change the oil filter when you change the oil.
The contentious points::shootout:
1) oil type - dino vs. synthetic
2) oil viscosity
3) oil filter brand
MY (and only my) opinion:
1) GO SYNTHETIC - I use Mobile1 5-30 in my '98 EB, and I am looking into using the AMSOIL brand.
*WHY* I like the ratings of the synthetics. I have done some looking around, and it seems like a good choice for me.
2) I use the manufacturers recommended viscosity.
*WHY* Well , I could bore you with all the technical issues of film thickness, bearing load, etc. (I am an engineer - not that it means anything), and the viscosity is picked to accomdate the expected loads and service. Its not for me to decide this.
3) I dropped using FRAM (guess I need to update my sig), and am now using Purolator. WIX is another good one. I determined this from again trolling the forums. I also found a great link to a oil filter study that I can't find (sorry), but will post when I can retrieve it.
4) I change the oil and filter every 3k - 5k. Some folks say you only need to change the filter after 2-3 oil changes. Some folks say you don't need to change anything for 8K - 15K
*WHY* Its is just plain cheap insurance to change this stuff often. It also gets me under my truck to check things out more often then less.
I also put in a FRAM quick drain valve (there are a few others out there), so it is just plain easy.
I hope this helps
