I am running into the same issue time and again. It may be too broad of a question, and it may be heavily opinion based, but I still wish to bring it up.
First off, I am trying to use articles from credible journals for my answers. However, it does happen that I simply can't find the proper material in the literature. For example, specific information on anatomical features, the side effects of drugs, or the specific symptoms of diseases are notoriously difficult to dig up without the availability of appropriate textbook or reference works. Or, to provide an example for all the Cell Biologists and Geneticists here, imagine you have to dig up how to prepare all the various solutions needed for a home-brewn fenol DNA extraction without Maniatis at hand. Would you sift through articles to find the one that happens to include the composition of all the buffer solutions and organic solvents?
Personally, I am hesitant using wikipedia as a source for the basis of my answer, as it may potentially list unfounded and unreferenced stuff, and sometimes even plain fallacies*. This aside from the fact that many wiki pages are either too elaborate (popular ones such as 'Neuron') or very short and unintelligible (unpopular ones such as 'Bipolar neuron'). lasrt but not least, it is kind of a dynamic website, so info may become deleted or changed. So the many comments placed under questions with a wiki page linked and the message 'Have you done any research?!' are not too useful in my opinion, but that aside.
There are other sources from which I simply do not know the credibility, but that do pop up a lot in my searches and seem credible but I simply can't assess whether they are worthy sources. I will add a list hereafter of typical examples. I prefer not to use them, or only sparingly and reluctantly in my answers**. I would, however, love to use them freely given the amount of information they contain. Moreover, I have noticed that other people use them quite frequently as a basis to back up their answer (e.g., Mayo Clinic is often used). If folks could shine their light on the value of these sources that would be really helpful:
- Wikipedia.org {Probably/arguably the most referenced source at Biology here. Personally, I avoid using it, but I have put it into the list for discussion}.
- Encyclopedia Britannica.com {wikipedia-like, but not open-access, i.e., not everyone can add stuff. It's a paid site when one wants full access}
- Drugs.com {encyclopedia-like site on pharmaca}
- Mayo Clinic.org {a site from a nationwide US clinic with a lot of accessible and interesting information, but directed to patients, not health care providers}
- WebMD.com {a site with descriptions of diseases and pathologies}
I might be adding a few more sites, but these are the most important ones, or at least give a fair idea of the type of sites I am referring to.
*However, I do use wikipedia to link specific words to explain jargon.
**University websites I use without much hesitation. For example, web pages of labs associated with credible universities.