Giving credit where credit is due...

Hi,
a bit slow today so thought I'd bug you all for opinions about proper crediting of sources.

I think I am defining a source as any entity that provides information or products that I use to accomplish my coding activities.

So, while building my little web application:
1. What sources should be credited?

2. How should sources be credited on a web application?

3. Should I worry about getting permission directly from the source?

As I am learning php by building a little application and web site, I am accumulating alot information, samples and products from various sources. And I am keeping a running account of these for inclusion on a specific web page (and, for some, a special Hotlinks list)

So what is the "proper" way to credit sources?

For Codewalkers.com (for example) I want to send an email request to the Site Admin for permission to include a site link and ask if they want to include a logo with the link. The link would contain a blurb about what was provided by the source.

But other sources only list a name in a text file.

Most sample code files aren't used verbatim, but provide ideas/techniques on solving issues. Do I credit those too? The list will be huge. hehe

Another example, that I think is kinda of funny... I will be using a JS calendar function that I got from Source Forge. But the email address for the source was closed for abuse. I am not sure what to do with that. Definitely need to cite the source, but what will be people think of my using the work of an email abuser? Har!

Anyway, your opinions are helpful, so thanks.

Whoops!
Coulda sworn I was logged in when I posted this...
Anyway, ...

Personally I cite whomever I take actual code from and anything whose licenses require me to cite them. People I get ideas from I don't normally cite - unless their idea was a major component of my project and I could never of done the project without it.

Getting permission directly from the source... I would only do that if the work didn't have any particular license attributed to it (though IIRC unless they note "all rights reserved" it is considered public domain if it is on the web). Most people like to know someone is getting value from their code.

I tend to cite all these people in the opening of my code in a comment box. I also try to make sure any web addresses or email addresses are included if they were provided to me, as well as notices required by their licenses.

One last thing - pay attention to licenses... using code from a GPL licensed work in a Creative Commons licensed work may not be allowed if the creative commons allows commercial derivatives (for example). Something like that - you would need specific authorization from the author.

Wow - that was a hodge podge.