My own approach, and you can take it with as large a pinch of salt as you like, is as follows:
If we've been eating something for a long time, and we're talking evolutionary scale here, then it's reasonable to assume it's good for us. The reason being that over time the variants of our genome that didn't cope well with that sort of food will have gradually got weeded out of the gene pool. If it's a fairly new kind of food, however, this process won't have had time to work so it's pretty much a crap shoot. So yes, I said it - not all processed food is necessarily bad for you.
This means that things like meat, fish, eggs, fruit, veg, nuts, seeds are likely to be better than things like cakes, biscuits, white bread and doughnuts (although I hear the holes are quite slimming).
Notice though that I'm using words and phrases like "reasonable to assume" and "likely to be" - there's a couple of reasons: one, this isn't a hard and fast rule, it's only a rule of thumb, and two, the vast majority of studies done on the effects of various foods on health are based on observational studies. Many being quite poorly performed with little or no controlling for confounding variables.
Since you asked for websites, I'll give you a couple:http://www.thelivinlowcarbshow.com/shownotes/
^ Jimmy Moore runs a near-daily podcast where he interviews a wide range of people. He's a guy who at one point weighed 410 pounds and has since then lost over 150 of it. It has a strong low-carb slant, which you may or may not find to your taste, but one advantage of it is you can download the podcasts and listen to them whilst doing other things (ironing, driving, etc). There's a huge archive going back a few years so you may want to be selective!http://www.marksdailyapple.com/
^ Mark Sisson's site runs regular articles on healthy eating. His bias is towards what he calls "primal eating" and overlaps very much with my definition of healthy eating that I gave above.
The good things about both sites is both are quite accessible, being written for busy lay people. Both of them are also very open-minded about opinions that differ from their own.
Oh, and if you have any specific questions on areas of nutrition that you want good answers to, this forum has a few knowledgeable and helpful people on it: index.php