3: God's number; well, one of God's...
6: man's number; if you don't me, take any fact about man and society; there's a big chance any number you churn out can be divisible by 6; case in pt; man has 6 qts of blood; has 6 main sections to his body, has 12 months in a year, has 24 hrs in a day, has 60 min in an hour and 60 sec in a min... etc, etc... interesting, eh? and man is given 6 days to work
7: the number of completion; Revelations is chock full of the number 7
now here's a new one you won't expect if you're hiding under a rock like me:
11: the number of urgency

you'd be surprised how many numbers you take pertaining to 9.11 has the number eleven in it...

also, i found this site, trying to search out meaning for revelations in the bible:

List of links

take with a grain of salt though; i haven't explored all the links, but this one seems particularily interesting:

link

mark of the beast

i find the 2nd link to also be very interesting; it not only lists some of the trademark things of the end times(mark of the beast, the antichrist, false prophets, etc), but lists some headlines which chart the progress of how we are progressing towards those end times