Comcast may have it online at http://www.xfinity.com/Customers/Clu/ChannelLineup.ashx
Service Centers should have printed channel lineups. Check locations and hours at http://customer.xfinity.com/service-center-locations to pick one up, or call Customer Service at 1-800-Comcast and have them send a lineup to you.
A typical Digital Economy lineup includes: Limited Basic/local channels, A&E, AMC, Animal Planet, BET, Cartoon Network, C-SPAN, CNN, Comedy Central, Discovery, Disney, E!, Food Network, Fox News, Hallmark, History, Lifetime, On Demand, truTV, TV Land, USA, The Weather Channel, and Music Choice.
That's for zip code 17401 in Central PA. Other areas should be similar, plus or minus a few channels.