I like gbulmer's suggested enhancements to serial monitor, and I would add one more – an option to send '\r' at the end of the string when the Send button is pressed to make it easier for a sketch to determine the end of an input string.
think that tabular output is needed as much with LCD as with Serial, so would want to see something along the lines of roypardi's suggestion that includes the ability to control the padding between fields so they can be lined up.
The ability to print multiple fields can be done now using a method published by Mikal Hart here: Arduino Playground - StreamingOutput
Its syntax is a C++ standard but I wonder if it looks a little scary to non-technical people?
so for me, the higher priority is something simple that can print a line at a time that includes control over the width of a field so printed values can line up on serial or lcd (or ethernet).