Spain’s .ES extension was originally introduced in 1988 but was only recently open for unrestricted registration as of 2005. Nic.es heads Spains domain registry and there are several registrars approved to sell .es domains. I know that 101domain.com offers a good price for .es at only $35/year.
Similar to many other countries in Europe, .es is heavily used within Spain by its local businesses, etc. Since 2005, many domainers have seen .es as a solid investment and some utilize the extension for domain hacks like beach.es.
The extension has made its mark in the reseller arena with some notable sales over the last year, here are a few of the top .es sales since Jan 2009, courtesy of DNJournal.com:
I expect that by the end of 2010 there will be at least one or two more six figure .es sales. I see more and more domainers investing in this ccTLD, a good .es marketplace I should mention is DonSubasta.com.