Best Camera to take on a round the world trip?

I would definitely recommend D5100 for its size and the price. It has many in-camera creative mode including HDR, which may be helpful on traveling as you may not be able to access to computers to process the photos all the time. It is very easy to use for new DSLR users and its small compact body is great for trip. Lenses I would recommend is somewhere between 17mm to 55mm like kit lens, but there's 18mm to 200mm, which range is awesome for both wide angle and telephoto use. I think if you have this range, you won't need any other lens to carry! Hope this helps! 

Nikon D5100 over D300s

-cheaper

-more MP

-better ISO performance

-lighter

-video

-flip screen.

For 800£ you can buy it with two lenses:18-105 (3.5-56)DX AFS lens and 35 or 50 (1.8) AFS. (based on http://www.amazon.co.uk prices)

D5100, because:

it is more lighter, and on a trip, it is a good thing

it has a flip uot screen, don't need to bend down, or take down the package to take a photo easily

it is more cheaper, but i think that D5100 has better image quality, cause D300 is an older camera

at night you can take photos with better ISO performance.

so, like sivko, i recommend D5100