The Hurricane Electric IPv6 Tunnel Broker service enables you to reach the IPv6 Internet by tunneling over existing IPv4 connections from your IPv6 enabled host or router to one of their IPv6 routers. To use this service you need to have an IPv6 capable host (IPv6 support is available for most platforms) or router which also has IPv4 (existing Internet) connectivity. their  tunnel service is oriented towards developers and experimenters that want a stable tunnel platform.

More info: http://www.tunnelbroker.net/

SixXS (Six Access) is a free, non-profit, non-cost service for Local Internet Registries (LIR’s) and endusers.
The main target is to create a common portal to help company engineers find their way with IPv6 networks deploying IPv6 to their customers in a rapid and controllable fashion. To reach these targets we are providing a whitelabel IPv6 Tunnel Broker and Ghost Route Hunter, an IPv6 route monitoring tool and various other services to help out where needed.

SixXS offers the RIPE, ARIN, APNIC, LacNIC and AfriNIC  communities pre-production deployment expertise based on the experience gathered while running the IPng IPv6 tunnel broker since 1999 combined with it’s successor, SixXS, totaling in more than 9 years of massive experience.

Most of the PoP’s are publicly available and provide free IPv6 connectivity to endusers allowing them to enjoy quality IPv6 connectivity. 10 Easy Steps to IPv6 describes how to quickly get going with IPv6.

More info: http://www.sixxs.net