Salutations to the Forum,
This thread is EXPERIMENTAL. The behaviour of this thread, the title of this thread, the contents of this thread, and this thread's very existence may change without notice in future (in fact I hope it will. Except for the last bit. Can't edit something if it's deleted).
The format is pretty simple. This thread contains links to other threads that discuss the problem in the title, offering solutions, references and so on. These separate threads used to be posts in one thread, but that thread ended up pretty big; and since URLs here can't use page-local anchors, the saving that would have come from using those wasn't available either. So each question has now been split into its own thread, accessible via this index.
These threads are open, so feel free to post if you think there's anything missing, other problems, details I've forgotten, further references, suggestions about style and layout (I'm terrible at style), or mistakes I've made. I'll go through now and then and combine those suggestions (with recognition) so that over time with community input this thread will become an invaluable resource for people looking for help.
If you want to write something similar - a survey of solutions to a particular common problem (with citations and whatnot), feel free to do so, post it, and PM me with the link. I'll check it out and see about adding a link to it here. If it's particularly long and detailed or specialised, of course, it would be better as a contributed article (the forum search engine doesn't cover articles, but I suspect they get higher traffic).
It's halfway to being a wiki. Kind of a moderated wiki.
Collected solutions to common problems.
Getting Help At All
Headers Already Sent...
Getting the browser to open a new window/in another frame/do something when I click the mouse...
HTML, images and/or attachments in email
Displaying three or four items per row (or column) in a table
PHP Bulk Email - Best Practices
Preventing Cross-Site Request Forgeries (CSRF) Exploits