The NYC marathon took applications from 90,000 runners for 50,000 places. The application fees are nominal, hence the excess demand. In this case, the essential ticket is the bib which runners wear, and the online market place has sprung into action. From Jennifer Blecher in The NY Times:
A New York City Marathon bib was offered on eBay last month for $750 with a "buy it now" option of $1,000. It went unsold, but two weeks later another sold for more than $450. Among the marathon bibs for sale on eBay yesterday was one for Chicago with a bid of $162. Most bibs for the New York City Marathon are selling for $100 to $200, but one seller on Craigslist was recently asking $775 for his bib for a man in his racing age group. People placing ads looking for bibs were offering up to $300.