I'm just a beginner at playin' steel. I have an early 60's Rickenbacker Electro 6-string console and it's tuned to C6 and a Melobar Rattler 6-string tuned to Open E. I've also played around with Open D on my Dobro.
You might want to search the forum for threads about tuning in the No Peddlers section. Everyone will give you a different opinion though. Some of it has to do with the kind of music you want to play. Check out Steiner Gregertsen's sound clips on his website. He's very talented composer/musician of the rock and blues variety. I think his website's down right now, but should be up again soon. Anyway, he generally uses Open D tuning and most people would tell you that Open D, Open E, or Open G are appropriate for rock or blues. I think one of the main reasons for selecting those tunings for blues is that if you have played slide guitar, then you'd already know Open D and probably the other two as well.
If you want to play country or hawaiian, then probably C6 would be the one that would be suggested. However, you can also play blues with C6. I think you'll find the majority of the current instructional materials in C6. This is the tuning that I'm concentrating on learning first for two reasons...the books and video instructional materials I bought are all in C6 and I absolutely love the sound of my Rick that's tuned to C6.
If you are more confused now, then join the club! (Just kidding!
) Here's a couple of good resources for non-pedal steel tunings:
Scroll down about half way on this page for 6-string non-pedal steel tunings.
http://www.scottysmusic.com/tunings.htm
Brad's Page of Steel has a lot of resources. This page has a lot of 6-string tunings, including several variations of C6. I think the most popular one is C6/A7. You will also find a link to one of the books that I purchased on this page: "Basic C6th Non-Pedal Lap Steel Method" by DeWitt Scott.
http://www.well.com/user/wellvis/tuning.html
Have fun!
Anita