There are several periodic trade conventions for online marketers. They attract both affiliates / publishers and advertisers.

A 4 U Expo Affiliate Marketing Conference & Exhibition - Held in London, and oriented towards European markets.

AdEaters

ad:tech - Versions in several cities around the world.

Advertising Week

Affiliate Convention - Entry is free for publishers.

Affiliate Summit - Mostly CPA / CPL focus.

AffiliCon - Based in Israel.

Data Marketing Show - UK.

DigiDay Networks

Digital Media Events

Digital Mission

eCommerce Summit

eMetrics Marketing Optimization Summit

Future Of Online Advertising (FOOA)

iMedia Connection Summits - Various events.

Interactive Advertising Bureau (IAB) - Holds an annual meeting.

Internet Week New York

LeadsCon - Oriented to lead generation.

Marketing Week Live - Based in the UK, and produced by Marketing Week magazine.

OMCAR - Based in India, and hosted by OM Careers.

Online Marketing Show - Based in London.

PPC Summit - Search marketing conference.

PubCon - Owned by Webmaster World. Oriented towards search marketing. There are US and European versions.

T.R.A.F.F.I.C. - Domain name expo. Sponsored by various marketing companies, including domain parking systems.