This is a website worth bookmarking. The excellent AskOxford has advice on grammar, spelling, commonly misused words and word origins.
You can whittle away some time playing word games (naturally these are educational and not to be confused with time-wasting).
There's even a fascinating QI-esque FAQ section, which ponders such questions as: Is 'deliverables' a real word? and What comes after once, twice, thrice?