From UO Resurgence WIKI

[c <insert text> -This will send your message to general chat on the shard. Everyone can see general chat.
[c -This will bring up the chat menu and will allow you to change options related to chat.
[pm <insert character name> This will send a private message to the character you specify
[motd -This will bring up the message of the day set by me.
[help - This will bring up all the commands currently available to you.
[password - this will allow you to change your account password. "balance"- When said to a banker NPC you will see the current balance of your gold in your bank box. This is the cumulative gold of all characters on your account.
"bank"- When said to a banker will open your bank box
"stable", "stall" -When said to an animal trainer NPC will bring up a target to allow you to stable a pet.
"claim list"- When said to an Animal Trainer NPC will bring up a list of all the current pets you have in the stables. You can also single left click next to your pet's name to remove the pet from the stables.
"guards"-When said in a guarded region will call the guards on any monster or player that is aggressive towards you.
"vendor buy" or "vendor sell"-When said to a vendor will show you a list the that vendor's wares or will show you what you can sell to that vendor
"I must consider my sins" -Gives you your long term and short term murder counts
"I renounce my young player status"- This will make your character not have young benefits anymore. Note that this happens automatically after 40 hours of gameplay.