I got the Poetic clear plastic back cover off Amazon for US$8. Looks good, the personalized engraving shows through well and the cover fits perfectly without adding too much bulk. Highly recommended.
For the screen I ordered a smart cover with the iPad, it's great but frankly a ripoff at $40! You can get an aftermarket one on Amazon for under $10 although I don't know how good they are.
No screen protector, I try to be careful and have had no problems so far. Might get one to reduce glare though.
I use a neoprene slipcase when travelling for extra protection in my luggage. It's the case that came with my netbook so didn't cost anything!