If you have suggestions to add to the list feel free to message or mail coirnav.Marcone in game.

ZAMEverquest allakhazam database. Reccommend running an ad-blocker or paying for premium. Otherwise you are going to have a bad time.
Brewall MapsBest maps I've seen much improved over mapfiend.
Zone Connection Map (Velious)Everquest zone connection map up to and including Velious. Courtesy of P1999.
Zone Connection Map (HoT)Old zone connection map up to House of Thule. Made originally by Samanna.
EQ InterfaceEverquest user interface list/downloads. Personal favorite is Savok's Vert.
Everquest TLP ForumsDBG forums, good luck.
EQItemsPretty useful site that can give you item choices based on your current gear or when looking for best in slot items. As a warning it's item rankings can sometimes be out of wack, but still nice info.
RaidlootAnother item database.
P1999 wikiNot 100% accurate for live but can glean some useful information especially with reguards to Plane of Sky.
Xanadas Progression Spell ListCurrently appears down 'in protest'. Hope to see it return.
EQTradersTradeskill database. Some things can't be made in early eras but still an invaluable tool.
Almar's GuidesSome of his content isn't for progression servers, but the tradeskill guides can be pretty useful.
Agnarr ProgressAgnarr server guild progress tracking.
Coirnav ProgressCoirnav server guild progress tracking.
Mangler ProgressMangler server guild progress tracking.
Phinny ProgressPhinigel server guild progress tracking.
TLP Community DiscordTLP community discord.