I am going travelling by bicycle, and I want to take a camera that allows me to take photos that are very high quality- e.g. raw format and with a good lense, and yet is not heavy, and is quite durable / resistant to dust. Do you have any recommendations for a good travel set up? I won't have the luxury of taking more than 2 lenses. In the past I took a Nikon D40x with an 18-200mm lens which was great but image quality was not quite up to scratch for what I want now.
I had originally posted this as a comment, but since the question has been edited to add "pro-quality" as the primary qualifier, I'm going to double-down and promote it to an answer.
The best solution for you is the Leica S-system. This will undoubtedly allow you to take pictures of very high, "professional" quality and has not just good but great lenses. Leica describes it as a "compact light-weight design", yet it's solidly built with the entire system (lenses and camera body) weather-sealed. There's a "compact all-rounder" (again, Leica's words) zoom you could take, and then for your second allowed lens, pick a prime that matches your favorite working field of view. (There's about a dozen to choose from, from ultra-wide to normal to telephoto.)
All together it'll only run you about $40,000, plus incidentals. That might seem like a lot, but hey, you want pro-quality, right?
That answer isn't meant to just be snarky. In order to provide a useful answer, we need more constraints. There are so many cameras on the market because there are so many different needs and situations, and "good for travel" doesn't really narrow it down since that's a huge segment of photography. But, even with specific information, this kind of question is hard to answer, because everyone will have their own favorite. It's better to ask questions that will help you make your decision, rather than asking us to do the shopping for you. (See this blog post for more on shopping questions.)
It's actually completely possible to produce top-quality images with the Nikon D40, even with that superzoom lens. It can certainly produce pro-quality images (where "image quality" is less important than other factors). The big, slow, compromised 18-200mm zoom is probably the biggest drawback equipment-wise, but even that should do if you're practiced at using it. Buying more stuff won't magically save you, but if you replace it with a nicer set of lenses you may find it easier. (That'd be an f/4 or f/2.8 constant-aperture zoom, or else a set of prime lenses, the latter being my personal non-sarcastic choice.) You'll still need to put in the effort to figure out how to get the best results, and fundamentally that will be the same as with the gear you had.
You might also find it nice to move to a more modern camera, and if weather and dust sealing is really the important criteria, you're looking at a mid-tier DSLR or mirrorless camera — see this search for current DSLRs or this one for mirrorless. You'd also need lenses to match — it happens that right now Pentax offers the cheapest weather-sealed lenses (and the cheapest weather-sealed DSLR body), but you'll also get it from higher-grade lenses in almost all systems.
If there are other technical features like that you're looking for, Neocamera and Digital Photography Review both have great search engines kept up to date with the latest models. Any modern DSLR will have big technology advances over a six-year-old camera like the D40, but that was a great camera with a great sensor, and, I have to emphasize again, to surpass the results you were getting with that, you'll have to do something different, not just use something different.
On a bike you need something that isn't too big ! there are specialist camera's out there, google found this fairly quickly http://www.amazon.co.uk/Extreme-Sports-Camcorder-display-detection/dp/B0081FF89E/ref=sr_1_8?ie=UTF8&qid=1359153885&sr=8-8
But if you a to use a standard camera, then I would suggest something that is not 'too' expensive in case it falls off so a canon G series or nikon P series.