What do all those different symbols before channels in a WHOIS mean?

There are few different symbols you may see prefixed to channel names in a user's WHOIS. These are:

@#channel
The user has operator status in the channel.
%#channel
The user has half operator status in the channel.
+#channel
The user has voice status in the channel.
<#channel
The user is invisible in a channel with channel mode +D or +d set.
-#channel
The user has user mode +d (deaf) set, and won't receive channel messages.
!#channel
User is a 'zombie', which means the user was kicked from the channel, but the kick has not yet been acknowledged by the user's server.
This FAQ entry's short URL is http://www.darenet.org/faq/16