The safest fonts (should be on all pcs) are: 

• Variable Width
• Fixed Width
• Times New Roman (Best for text)
• Arial/Helvetica (Best for headings)

I have found these fonts on most pcs:

• Bookman
• Courier (can be ugly)
• Garamond
• Impact
• Comic Sans
• Haettenschweiler (difficult to read)
• Verdana

Common fonts to all versions of Windows & Mac equivalent