In the United kingdom - political parties cannot advertise politically on radio or television. Instead political parties are allocated a certain amount of timed slots, in which they can present their case - these are known as "party political broadcasts". The time is free to the parties, though they must pay for making the broadcast. Keele University has a database of past election broadcasts available at http://www.psr.keele.ac.uk/area/uk/peb.htm. The legal limits are a major reason that political campaigning in the UK is significantly cheaper than in the US.
Stanford University maintains an online archive of US presidential ads - including the most recent. It is available at http://pcl.stanford.edu/campaigns/2008/