Error Handler provides a custom interface to error handling in PHP. Several report formats can be used to reveal what circumstances led to a certain error. One for logging, one for display, and one for redirection. It captures the errors and captures (to a customized level) the context and variables surrounding the source of the error and neatly organizes them as a series of reports.
Simple error handler class can be use to intercept and log PHP execution errors. The class provides an error handler function that outputs a stack back-trace with the functions, arguments, file, and lines of where an error occurs, as well the values of super-global variables $_GET, $_POST, and $_FILES, and also the IP address of the current user accessing the site. When used with a MySQL class that triggers PHP errors on a MySQL error, you can use it as a means to debug broken MySQL queries.
Xdump is a little PHP library which can provide full featured variable dumps. It requires the ability to show the source code around the line where the dump was invoked. It features contractible HTML+JS dumps. It shows nicely backtraces, including source code lines for every step. Reference checking is used to avoid recursion. It is object oriented and extendible.