Trade shows per year: 300 to 400

What's cool: Booths can link directly to an exhibitor's Twitter, LinkedIn, Facebook, or YouTube profile.

Recent shows: The RDH Event, a trade show for dental hygienists; Digital Marketing World, a conference about online marketing; and the Mobile 2012 Virtual Tradeshow, an event for the cell-phone industry

Trade shows per year: 300

What's cool: Unisfair supports 16 languages, including Chinese, Turkish, and Czech.

Recent shows: BlueLinx Virtual Buying Show & Knowledge Forum, an expo for manufacturers of green building materials; McKnight's Online Expo, an event for assisted living facilities; and Elearning! Summit 2009, a show about online corporate training tools

Trade shows per year: 250

What's cool: ON24 uses an attendee's profile to suggest relevant exhibitors.

Recent shows: Vaccine Virtual Congress, the virtual arm of a trade show for the medical industry; Telephony University, an event for the telecom industry; and the Oracle Partner eXpo, a show for Oracle resellers and vendors