Here is a list of all the usermodes which are available for use.

o = IRC Operator
d = Only receive channel PRIVMSGs starting with a bot command character (Deaf)
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
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
D = Only receive PRIVMSGs from IRCOps, servers and services (privdeaf)G = Filters out all Bad words in your messages with
H = Hide IRCop status in /WHO and /WHOIS. (IRC Operators only)
I = Hide an oper’s idle time (in /whois output) from regular users.
R = Allows you to only receive PRIVMSGs/NOTICEs from registered (+r) users
S = For Services only. (Protects them)
T = Prevents you from receiving CTCPs
W = Lets you see when people do a /WHOIS on you (IRC Operators only)
Z = Only receive/send PRIVMSGs from/to users using a Secure Connection (SSL)