Personally I'd rather not see yet another thread flaunting the word "broken" around. I get tired of reading that stuff after a while. It's generally easy to tell when something is broken in context, because things stop being fun for everyone.

The top of my preferences would be a "why this is a good spell" one. Generally spells are the harder part of the system for beginners to pick up on, simply because there's so many of them, and the only way to really learn about them is to read the descriptions. That can be a pretty daunting task, and even then, there are always traps, which look like they're good, but are not very good in practice. I think a guide of what to look for in a spell of a given level and why would be the most useful, for both a player and DM perspective.