The best way to get the look of text typed on a typewriter is ... to type it on a typewriter! You can then scan it and use it in a digital document.
However, there's also a place for "typewriter" fonts. On this page you will find several such fonts, which are free for personal or commercial use (I will enjoy learning how they are being used -- feel free to contact me). Just click on the name of the font to see its characters and the typewriter that created it, and to download it.
Technical details: these TrueType fonts were created using YourFonts.com and tweaked with TypeTool. In some cases I used a carbon ribbon or inked the type directly to get the clearest possible impression; sometimes I used a traditional fabric ribbon. You can make a typewriter font too: download the YourFonts.com template, and either type on it directly or use an application such as Photoshop to insert scanned images of typing from your typewriter. Note that these are all proportional, not monospaced fonts, even though most of them would be monospaced when originally typed on a typewriter. I'm not a professional font designer; I can't guarantee that these fonts will work with all applications, and probably cannot help you if you encounter problems using them on your computer (although you are welcome to let me know that you're having trouble).
You can find more free "typewriter" fonts at dafont.com.