Since it hasn't been mentioned yet, pretty much the best IRC search out is
http://searchirc.com - as you'll be able to find virtually any non-secret channel on any known IRC network...
I say this because:
1) SearchIRC does not have arbratary limits on networks, requiring them to have N number of users to get listed. All networks are included when possible.
2) SearchIRC lists ALL channels, netsplit.de and others only store channels with >N users, so they only have partial channel lists.
Check them out for yourself and compare.
