From the IRCd’s own description, here’s all the user modes:

• o = Global IRC Operator
• O = Local IRC Operator
• a = Is a Services Administrator
• A = Is a Server Administrator
• N = Is a Network Administrator
• C = Is a Co Administrator

• d = Makes it so you can not receive channel PRIVMSGs (Deaf)
• g = Can read & send to GlobOps, and LocOps
• h = Available for Help (Help Operator)
• i = Invisible (Not shown in /WHO searches)
• p = Hide all channels in /whois and /who
• q = Only U:lines can kick you (Services Admins/Net Admins only)
• r = Identifies the nick as being Registered (settable by services only)
• s = Can listen to Server notices
• t = Says that you are using a /VHOST
• v = Receive infected DCC send rejection notices
• w = Can listen to Wallop messages
• x = Gives the user Hidden Hostname (security)
• z = Marks the client as being on a Secure Connection (SSL)
• B = Marks you as being a Bot
• G = Filters out all Bad words in your messages with <censored>
• H = Hide IRCop status in /WHO and /WHOIS. (IRC Operators only)
• R = Allows you to only receive PRIVMSGs/NOTICEs from registered (+r) users
• S = For Services only. (Protects them)
• T = Prevents you from receiving CTCPs
• V = Marks the client as a WebTV user
• W = Lets you see when people do a /WHOIS on you (IRC Operators only)

Obviously, +V is the best user mode.

For channels:

• v <nickname> = Gives Voice to the user (May talk if chan is +m)
• h <nickname> = Gives HalfOp status to the user (Limited op access)
• o <nickname> = Gives Operator status to the user
• a <nickname> = Gives Channel Admin to the user
• q <nickname> = Gives Owner status to the user

• b <nick!ident@host> = Bans the nick!ident@host from the channel
• Extended bantypes (for more info see /HELPOP EXTBANS) [h]
• c = Block messages containing mIRC color codes [o]
• e <nick!ident@host> = Overrides a ban for matching users [h]
• I <nick!ident@host> = Overrides +i for matching users [h]
• f <floodparams> = Flood protection (for more info see /HELPOP CHMODEF) [o]
• i = A user must be invited to join the channel [h]
• j <joins:sec> = Throttle joins per-user to ‘joins’ per ‘sec’ seconds [o]
• k <key> = Users must specify <key> to join [h]
• l <number of max users> = Channel may hold at most <number> of users [o]
• m = Moderated channel (only +vhoaq users may speak) [h]
• n = Users outside the channel can not send PRIVMSGs to the channel [h]
• p = Private channel [o]
• r = The channel is registered (settable by services only)
• s = Secret channel [o]
• t = Only +hoaq may change the topic [h]
• z = Only Clients on a Secure Connection (SSL) can join [o]
• A = Server/Net Admin only channel (settable by Admins)
• C = No CTCPs allowed in the channel [o]
• G = Filters out all Bad words in messages with <censored> [o]
• M = Must be using a registered nick (+r), or have voice access to talk [o]
• K = /KNOCK is not allowed [o]
• L <chan2> = Channel link (If +l is full, the next user will auto-join <chan2>) [q]
• N = No Nickname changes are permitted in the channel [o]
• O = IRC Operator only channel (settable by IRCops)
• Q = No kicks allowed [o]
• R = Only registered (+r) users may join the channel [o]
• S = Strips mIRC color codes [o]
• T = No NOTICEs allowed in the channel [o]
• V = /INVITE is not allowed [o]
• u = Auditorium mode (/names and /who #channel only show channel ops) [q]

• [h] requires at least halfop, [o] requires at least chanop, [q] requires owner