What's a good Word processor and spreadsheet app for iMac that is freeware?
There's not one answer. There are several answers, depending on your needs and personal preferences.
If you need/want full MS Word compatibility, then the obvious choice is Microsoft Office Word 2011. It is a full-featured word processor that can handle any task.
If you don't need all the advanced word processing features of Word, but you want some degree of compatibility while being more elegant and designed towards desktop publishing and the creation of stylish documents, then you should try Apple Pages.
If you want a Mac-only full featured word processor with Word compatibility, then you may like Nisus Writer Pro.
If you wish to write long and complex documents seamlessly, and do not need full compatibility with Word, then Mellel might be for you.
If price is a concern, but you don't want to give up the whole set of features or compatibility with Microsoft Office, then you should download OpenOffice or LibreOffice (well, you should download both anyway, as they are free).