Pretty hard to choose just one band as the greatest of all time. I would however have to agree. To date I'd have to go with Zeppelin as the tops. All the live performances I've seen and heard of them are incredible.
As a side note I'd recommend checking out mrlayance's website
www.hipbase.com to any fan of The Tragically Hip or anyone else just looking for info about another great band. Tune into the hipbase radio for some great tunes.