In addition to the profiles on the Prospects site there are various sources of information regarding marketing roles. The Chartered Institute of Marketing has a dedicated careers section getin2marketing which incorporates a range of job profiles and includes a database of related graduate schemes and placements.
In the Target Jobs Marketing Section you will find a useful insight in to the various Marketing and Advertising roles available, as well as internship/placement and graduate-level positions to apply for.
Additional sources of Marketing vacancies:
Some sites have job vacancy listings and also a 'directory of members' which can prove to be effective sources of information on companies to whom you may want to target a speculative application. Using trade journals and professional associations can help you keep up to date with current issues in the industry, something that is highly valuable when you are preparing for applications and interviews. you will need to show an awareness of different brands and campaigns, and may well be asked about this at interview. You can find lists such as the Top 100 Power Marketers and the Top 50 Advertising and Marketing Agencies, which will give you a real flavour of the the organisations making an impact.