Invision Power Board is one of the best commerical forum script available today in the market.

JCInk is offering this free IPB forum hosting facility for its members. They are using Invision Power Board v1.3 Final for forum hosting. Their uptime stats say that they are having more than 99% uptime.  They have it customized to give improved performance on their servers.

If you are interested, try them at http://ipbservice.jcink.com/