I can't believe it's taken Google this long, but there's finally a (not-quite-perfect) solution: Message Sneak Peek, which shows you the contents of any e-mail when you right-click it. Take a look:
This is actually a one-click function: It's not like a traditional right-click exercise where you're shown a menu and then choose the option you want. Just right-click any message and bam, there's the "peek" window.
Unfortunately, that's all it is: a peek. The pop-up preview lacks a scroll option, so you get to see only the first dozen lines or so of the e-mail. That's a rather maddening oversight.
On the plus side, the window does include both Archive and Delete buttons, both handy time-savers. And until Google gets a clue and adds a bona fide preview pane to Gmail (seriously, Google, take a peek at Yahoo Mail), this is definitely a step in the right direction.
More on BNET: