The first couple of shortcuts (which I use dozens of times a day) are Command–Left Arrow and Command–Right Arrow. These will take your cursor to the beginning or end of whatever line you’re typing on.
As that extremely lovely screenshot demonstrates, my cursor’s in the middle, but pressing Command–Left Arrow will move it to the beginning of the line and Command–Right Arrow will move it to the end.
Similarly, the Command–Up Arrow and Command–Down Arrow shortcuts will place your cursor at the beginning or the end of your document, Mail message, or what have you.
Be aware, though, that if you’re in a text box in Pages, those shortcuts will move you to the beginning or end of the text box instead of the whole document.
Finally, the last couple I use frequently are Option–Up Arrow and Option–Down Arrow. Those will take you to the beginning or the end of the paragraph that your cursor’s in.
And as promised, here’s the giant list of shortcuts you can use on text. This link is supposedly specific to Pages, but as I noted, most of the shortcuts actually work all around your Mac. If you don’t feel like going through the entire list, be sure to check out the section on selecting text—it’s pretty awesome to know how to use keyboard shortcuts to extend a selection you’ve made without having to drag your cursor around. Plus, it makes you look like a wizard, which is always a good thing.