Honestly I am staying away from 3D until the content pipeline is released. I know I am not the only one that is waiting.
I have seen many XNA projects and I think we as a community have not yet mastered the art of 2D games.
True, the content pipeline is probably worth waiting for, last I heard is that another Beta release is/was meant to be released with the content pipeline included, although I'm not too certain that was official. Anyway, I'm waiting for the final release for the CP, although there are some tutorials on http://www.xbox360homebrew.com .
Good Luck.
Learn to use a shader based language. The rendering is 100% shader based in XNA I guess this is good in a weird sort of way you don't have to worry about being stuck in yesteryears of 3d game programming.
I'm coming from OpenGL and its a bit odd to not have anything like a quadlist or quadstrip. I suggest reading around on scene mangement and animation basics. Which if you've masterd 2d you should have framed based animation down which will most likely what you'll use.
Also prepared to get creative there seems to be no way to transform things at least not with my playing with it. The way i've done it is looking at the examples with the generic transform shader. Which takes a matrix which you can crate any type of transformation from that and apply it as an effect. Which is a weird way of doing it for me. I'm still playing with multiple effects and such. A very good place to start is their 3d FAQ which tells you how to draw primitives (which are just triangles strung together). Look at spacewars starter kit for model loading though the content pipeline will help you greatly with managing your art assets.
Gamasutra has some neat articles on a postprocessing framework which will give you information on creating those cool post processing effects like bloom, motion blur and other things like. After a bit of practice with this I might put a few tutorials together. This is a very neat framework and poses an interesting challenge to 3d developers.
the content pipeline to be fixed. If you cannot wait though you can
have a look in example at Kukyona's work, which has created a basic 3D
terrain engine. No fancy stuff going on, but it does show what you can
do with XNA already. To see his work in action:
http://kukyona.blogspot.com/
Another sample is the free floating
camera control which can be found on the following site:
http://crenna.spaces.live.com/blog/cns!1DB5AC7D2F969F08!182.entry
There
are more out there, in example see the xbox360homebrew.com tutorials
listing, but it is probably best as said to stick with the 2D work for
now; master it to begin with and wait for the 3D pipeline to be
officially fixed.
Asides from these basic code samples there are
no true tutorials for which you asked as far as I know off. Although
some give a basic introduction to some 3D work, it doesn't really get
you into the 3D work, simply due to the fact that the pipeline isn't
ready yet, for exploring purposes it's nice to go beyond 2D, but there
it ends; once official support for 3D is there and functioning the 3D
tutorials and along with that books covering the subject will be within
handreach for you.