[SunHELP] ISP-Web URL screening.

Dear Solaris fellows,
Today I got homework from my boss.
As ISP with thousand, what are possible good ways 
to blocks the blacklist of URL (ex. www.sex.com), so
my customers will not able to surf that black-list web site.
-- What I though is block at web-cache (because we have L4 for port80).
-- block the blacklist IP at core-routers,switch.
-- Is there any central database store blacklist URL, like as open relay
db.?

Let's share your experience and idea, or point me
resource, link, paper whatever.
please show platform,product, solution, 
THanks in advances
Merry Christmas to you all.

Pat.