In reply to rallymania:
I wouldn't be without my Cokin ND grads, love 'em for sea/landscapes although I don't tend to shoot many! Lenspen or similar is also a worthwhile investment. I can highly reccomend Tamrac backpacks.
As for batteries I have 1 Nikon one and the rest of no-namers that outlasts my original Nikon one. I had a grip on my old camera and whilst I love them for studio portrait shooting it's just more bulk when out and about. Bear in mind that most battery grips will still need you to buy the extra batteries to go in them.
Think carefully if you really want a polarising filter; a decent circular polariser will hit the wallet fairly hard, especially if you don't need it. I'f you're worried about your glass then I'd definately say get a screw-in skylight filter to preotect the front element.
If you're going DSLR then I'd shoot raw; which means getting software to edit raw files into jpgs; maybe one of the Canon mob can tell you whether the software comes bundled, I know it doesn't with Nikon bodies. I'm currently using Photoshop Elements and it does pretty much all I need.
Happy snapping!