Just because a font (or collection of fonts) is free, doesn't mean it's not copyrighted. It is unethical and illegal to violate someone's copyrighted work. Most fonts come with some sort of license. Though that license may give you unrestricted use of the font, many don't.

Commercial fonts (and even many non-commercial fonts) come with a EULA; End User License Agreement. Some of those EULAs have restrictions on your use of the fonts you may never have thought of.

Read The Law on Fonts and Typfaces at crowdSPRING, Font Licensing at the Free Software Foundation and Free Fonts: Free is not always Free on The FontFeed.

Many font collections are available through apt-get. There are hundreds of fonts available this way. The first thing to do is enable the partner repositories.
Go to Menu --> System Tools --> LXTerminal
Type (or copy and paste):
sudo add-apt-repository "deb http://archive.canonical.com/ $(lsb_release -sc) partner"[Enter] or [return]
You can get a list of installable fonts through apt-get by searching for packages beginning with fonts- or xfonts-
For most font collections, type (or copy and paste):
apt-cache search fonts | grep '^fonts-'[Enter] or [return]
and/or for Console fonts
apt-cache search fonts | grep '^xfonts-'[Enter] or [return]
Then sudo apt-get install fonts-name-of-collection

Some of the many font collections:
fonts-beteckna (San-Serif TrueType Futura Like Font)
fonts-breip (Handwriting Font)
fonts-dustin (Various TrueType Fonts)
fonts-larabie-deco (Decorative Fonts)
fonts-larabie-straight (Straight Fonts)
fonts-larabie-uncommon (Uncommon Fonts)
fonts-liberation (Times, Arial and Courier Like)
fonts-pecita (Handwriting Connected-Letter Font)
fonts-tomsontalks (Comic Letters)
Update your list of fonts already installed by refreshing the font cache
Type (or copy and paste):
sudo fc-cache -fv[Enter] or [return]

The "core" Microsoft non-free font collection (including fonts you may love or hate, but may want to install for others' sake: Andale Mono, Arial, Arial Black, Comic Sans MS, Georgia, Impact, Tahoma, Times New Roman, Trebuchet,  Verdana and more) is available through apt-get too. sudo apt-get install ttf-mscorefonts-installer During installion; you will be greeted with a impossible-to-ignore EULA agreement.

Microsoft Core Fonts EULA
[Tab] to <OK> then [Enter]
EULA Part 2
[Arrow Left] to <Yes>

Over 500 font packages are available through the Synaptic Package Manager. Click the ones you want (or want to try) and select "Mark for Installation." If you agree to install the fonts you've chosen, hit the "Apply" checkmark.

Synaptic Apply 

Thousands upon thousands of fonts are available on the Internet. There are many, many websites that specialize in Fonts. Commercial pay-for fonts to absolutely no-restrictions public domain fonts and everything in between.

Many websites featuring downloadable fonts and font families only offer a choice between Windows and Mac (no GNU/Linux/*buntu). Compatibility with Lubuntu is most assured (easier) with Windows TTF or OTF fonts.

The following is a sample of free font sites available:

1001 Free Fonts
Abstract fonts
Font Squirrel
Free and Open Source Fonts
Free Font Manifesto
Google Fonts
Lost Type Co-Op
Open Font Library
We Love Icon Fonts

Download Fonts from the Web

The fonts you download from a website will appear in your Downloads folder, on your Desktop, or wherever else you specify. Where to put fonts to make your system see them is discussed at length here: FONTS FOLDER