Here's what the EQ2_UI_Customization.doc says:
Sounds
Any of the following sounds can be replaced per skin or per client. The list is definitely subject to change.
To replace a sound, add a wave file with the sound name in the sounds subdirectory.
EQ2/UI/Default/Sounds – to replace the sound for all skins on the client
EQ2/UI/CustomUI Folder/Sounds – to replace the sounds for a particular skin
Name - Description
Broadcast - Used for SOE broadcast messages
Buy_failed - Unable to purchase item
Click - UI click 2
coin_cha_ching - Purchased item
ding - DING!!!
encounter_broken - Broken encounter
frontend_pressed - UI click 1
inventory_attune - Attune item
inventory_cant_equip - Unable to equip item
inventory_destroy_item - Destroy item
inventory_equip - Equip item
inventory_un_equip - Unequip item
loot_failed - Unable to loot item
moveable_object_place_failed - Unable to place item (ie, house items)
place_item - Successful item placement (ie, house items)
quest_item - Quest item found
skill_up - Skill increase
spell_gained - New spell learned
too_far - Too far away from target
trade_accept - Trade accept
trade_propose - Trade offer
ui_chestdrop - Chest drop from NPC on death
ui_friend_logoff - Friend logoff alert
ui_friend_logon - Friend logon alert
ui_guild_lvl_up - Guild DING
ui_invite - Invite to group alert
ui_joined - Joined group alert
ui_pressed - UI click 1
ui_spirit_lvl_up - Tradeskill pristine item creation
ui_tell_receive - Incoming tell
ui_tell_send - Outgoing tell
ui_tradeskills_lvl_up - Tradeskill DING
war_drum - Slayer update
waypoint_activated - Waypoint alert
ui_mail_have_unread - Unread mail
ui_mail_send_success - Mail sent
ui_mail_send_failed - Mail send failed
ui_mail_deleted - Mail deleted
ui_mail_open - Mail open
ui_guild_logon - Guild member logon alert
ui_guild_logoff - Guild member logoff alert
ui_window_book_open - Knowledge book, Guild window, etc
ui_window_inventory_open - Bags, Inventory, etc
ui_window_main_open - Options, Friends, etc
Hope this helps