Speckie is an easy-to-use and very helpful real-time spell checker for Internet Explorer.
The program works in any regular web page text box. Just start typing, and if you mis-spell a word and you should see a red line immediately appear beneath it, Word-style. Right-click the highlighted error for a list of possible alternatives, choose the one you need, and Speckie will replace the original text accordingly.
This seems like it would always be useful to us, but if you want to turn off spell checking temporarily for some reason, then just right-clicking the text box and clearing the "Check spelling" option will make it happen.
And another right-click option, Dictionaries, lets you replace the default US English dictionary with a number of downloadable alternatives: British and Australian English, Dutch, French, German, Italian, Spanish and more (the Speckie site has the full list).
The program also has a few configuration options available (click Tools > Speckie Options). You may want to select "Enable spell check in single line edit fields", for instance, as this is turned off by default. And if you don't like the default wavy red line to highlight errors, then that's not a problem, you can quickly choose a different tag style and colour here.
Note that this is a specific version for Windows 8.