but they have limited use as their topics are not things that show up all the time. But for the most part Wizards doesn't have books that are for everyone. They do though have good quality books on topics that some people will need and want so fogure out what your needs are and then find the books that fit them.
Expanded Psionics Handbook
Unearthed Arcana
Book of Fiends (Green Ronin)
Advanced Bestiary (Green Ronin)
The Book of the Righteous (Green Ronin)
Dynasties & Demagogues (Atlas Games)
Iron Kingdoms Character Guide (Privateer Press)
Iron Kingdoms World Guide (Privateer Press)
There are others but that's what's at the top of my list.
Battlebox (Fiery Dragon)
Wilderlands of High Fantasy (Necromancer Games)
Grim Tales (Bad Axe Games)
Monsternomicon (Privateer Press)
A Magical Medieval Society: Western Europe (Expeditious Retreat Press)
Tome of Horrors (Necromancer Games)
Draconomicon (WotC)
Besides that- it depends on game world, gaming style, dm vs player and so on.
As an Eberron player I would say the Campaign book is critical. There are speciality books already mentioned that are important. I am also enjoy the Tome of Horrors monster book.
For the DM, I really like Monsters of the Boundless Blue and a subscription to Dungeon Magazine.
I'm using the full e-tools package more and more these days too.
I loved Dog Soul Publishing's Baba Yaga book. I'm probably going to run a PbP using it.
If you want to make your own monsters, then A Magical Society: Beast Builder is unbeatable.
For players, I second the Battelbox motion.
Obviously your own PHB is a must as well.
Your best bet is to click over to the Reviews section of the site, and start reading.
The review section can't be sorted by rank, and AFAIK doesn't include gaming aids.
So far, I've really liked the suggestions of: Lords of Madness, Monsternomicon, Advanced Bestiary, Dynasties and Demagogues and, the Magical Mideval Society book.