In the UK, there is is a thick book, many libraries have it, BRAD Media
Brad = British Rate & Data
+44 171 505 8287
and in the states a similar service is offered by SRDS (contact details).
This gives circulations, ratecard costs of various ad sizes, commercial
for all us cyberjunkies, for the US, www.mediafinder.com and in the UK www.mediavillage.co.uk are on the internet.