..For landscape and portraits, I'd be perfectly happy with a 600D and some nice glass, though if you really never shoot moving subjects I'd suggest the 5D Mark II. You shouldn't buy anything until the dust settles after the D600 hits.
A lot of good advice has been offered so far, and some tripe.
You'll take the best shots with a system you're comfortable with, any system. So use what you like.
but be aware of the differences and let that also guide you depending on what you want to do with your images.
Small prints or on-screen, doesn't really matter.
BIG prints... I'll lean towards my Nikons because...
When it comes to post-processing my images I can get more out of my recent Nikon bodies' raw files than I can from a Canon raw file. But this only matters when the shot I'm taking is something the Canon is weak at and I can only really say there is one circumstance where I will pick Nikon, no contest -
Landscapes under challenging lighting conditions.
I would describe this as a high dynamic range scene with full sun illumination and (large) parts of the scene in deep shadow.
IF you want to bring up the shadows then the Nikon's low ISO files are lower noise and post-process better.
Otherwise you can shoot really good landscapes with Canon too. I tend to prefer Canon color rendition, overall handling and most of their lenses. Plus their free DPP software works very well for basic processing and adjustments of your raw files.
I prefer my Canons for portraits and most general shooting
I prefer my Nikons for landscape and artistic work where I'll be doing more post-processing to create the final image.
LostArk is right about this, wait until after Photokina announcements and keep watching for more rumors of soon-to-come hardware because there's a dustup coming with Canon trying to counter the various body-slams from Nikon this year.
FWIW, I'm not really happy with the 5D Mk II, it's noisy and can even show some banding noise in midtones and sky under proper exposure. It's a decent camera, and a very cost-effective full frame one that can still produce some great images but its files can also start to fall apart pretty quickly under extensive post processing.