Arial

Simple and most popular among websites

Times New Roman

This is the defont for most websites...ha, see what I did there, deFONT instead of default

Courier New

This is resembles a typewriter

Verdana

This is basicly a larger version of "Arial"

Trebuchet MS

Mainly uses for large headers

Georgia

Basily a largr version of "Times New Roman"

Century Gothic

Mainly for headers, not so much main text

Lucida Sans Unicode

Best known for its use in Macs

Palatino Linotype

This is inspired by renaissane lettering

Comic Sans MS

Used for more ligthearted sites.