This is by far the longest version of this list I've seen. It was compiled by me from various sources but I can't take credit for any of the contents (or any errors contained therein).
Enjoy.

 

660: Approximate number of The Beast

-666: Negative number of the Beast

6/6/6: Date of the Beast

667: Beast's Dozen

DCLXVI: Roman numeral of The Beast

666, 1332, 1998, 2664: Years of the Beast

666.0000000000: Number of the High Precision Beast

0.666: Number of the Millibeast

/ 666: Beast Common Denominator

0.005015: Reciprocal of the Beast.

666 ^ (-1): Imaginary number of the Beast

1010011010: Binary number of The Beast

-0.80902: The Sine of the Beast

443556: Square of the Beast

25.807: Square root of the Beast

295408296: Cube of the Beast

0.58779: Cosine of the Beast

-1.37638: Tangent of the Beast

2.8235: Log of the Beast

6.5913: Ln Beast

1.738E289: Anti-log of the Beast

6.66E2: Scientific number of the Beast

29A: Hexadecimal number of the Beast

666!: Factorial of the Beast

2, 3, 3, 37: Factors of the Beast

13320: The League of the Beast

95904: A gross Beast

665.5-666.5: Range of the Beast

(665, 667): Open Interval of the Beast

669: Sexual Position of the Beast

670: Beast rounded up

6, uh... what was that number again?: Number of the Blonde Beast

1-666: Area code of The Beast

00666: Zip code of The Beast

Mailto:666@hell.org: E-mail address of the beast

http://www.666.org: web-page of the Beast

Lotus 6-6-6: Spreadsheet of The Beast

Word 6.66: Word Processor of The Beast

6.6.6b6: Version of the Beast

Windows 666: OS of the Beast

i66686: CPU of The Beast

666 Mhz: Bus speed of the Beast

665.99996973: Number of the Beast on a Pentium

chmod 666: Makes the Beast writable and executable

umask 666: File access rights of the beast

chown 666:666 foo: uid and gid of the beast.

1-900-666-0666: Live Beasts! One-on-one pacts! Call Now! Only

$6.66/minute. Over 18 only please.

1-888-666-6666: Toll free number of the Beast

$665.95: Retail price of The Beast

$399.96 (net) $359.86 (30 days): Wholesale Price of the Beast

$55.50: Monthly cost of the Beast in twelve easy equal monthly instalments

$699.25: Price of The Beast plus 5% state sales tax

$769.95: Price of The Beast with all accessories and replacement soul

$656.66: WalMart price of The Beast

$646.66: Next week's WalMart price of The Beast

$0.66: Ground Beast per pound

Phillips 666: Gasoline of The Beast

Route 666: Way of The Beast (Highway to Hell)

666 Minutes: Weekly news program about the Beast

666 F: Oven temperature for roast Beast

66.6 mHz: FM station of the Beast

666 kHz: AM Station of the Beast

664 & 668: Neighbours of the Beast

666k: Retirement plan of The Beast

666 mg: Recommended Minimum Daily Requirement of Beast

6.66%: 5 year CD interest rate at First Beast of Hell National Bank, $666 minimum deposit

999: A Beast and a half

666i: BMW of The Beast

666 Sunset Strip: TV series about the Beast

DSM-666 (revised): Diagnostic and Statistical Manual of The Beast

66.6: A Mini-Beast

665.9999...: The Beast's Twin

WD-666: Spray Lubricant of the beast

IAM666: Licence Plate of the beast

333: Half brother of the Beast

Formula 666: All purpose cleaner of the Beast

666-66-6666: Social Security number of the Beast

6666 6666 6666 6666 EXP 6/66: Credit card of the Beast

666 lb CAP: Weight limit of the Beast

6-6-6: Fertilizer of the Beast

6-666-66666-6: ISBN # of the Beast

0-449-13070-3: ISBN # of 'The Number of the Beast' by Robert A. Heinlein

2666: The ELO rating of the Beast

667: The Beast's number will be up when Christ returns

66-66-66: Bust, waist and hips of the Beast

66.6: Atomic weight of the Beast

666 Kelvin: Air conditioning of the Beast

66 for 6: Cricket score of the Beast

666> . . < 666: Beast coming out me ears after that little lot

666666: Power of the Beast

66 to 6: Typical Beast Football score

666.6.b6.66: Beta version of the Beast

"666: Minutes of uninterrupted music" -- Radio Show of the Beast

"$666: Doctor's Bill of the Beast

"$1332": Lawyer's Bill of the Beast

"Algebra 666": College Class of the Beast

Fahrenheit 666: Ignition temperature of the Beast

666th Airborne: The Armed Forces unit of the Beast

(666) 666-6667: Wrong Number of the Beast

666B: Neighbour of the Beast

Sick, sick, sick: Humour of the Beast

3/4, 6/8, 4/4 - the number of the beats (any key you like, lots of power chords)

666 Bottles of Beast on the Wall

Mazda 666: Economy car of the Beast

Boeing 666: Airplane of the Beast

No. 666: Pencil lead of the Beast (for forms and standardized tests)

A 666: Tuning pitch of the Beast

Chanel No. 666: Fragrance of the Beast