Free

1. 1001 Free Fonts - http://www.1001freefonts.com/
2. Dafont - http://www.dafont.com/ (one of my favorites)
3. Font Space - http://www.fontspace.com/
4. Free Premium Fonts - http://www.freepremiumfonts.com/
5. Google - https://www.google.com/fonts (one of my favorites)

Paid

1. Fonts.com - http://www.fonts.com/
2. Linotype - http://www.linotype.com/
3. Lost Type - http://losttype.com/browse/
4. MyFonts - http://www.myfonts.com/

Free and Paid

1. 1001 Fonts - http://www.1001fonts.com/
2. Font Squirrel - http://www.fontsquirrel.com/