Other must have PS2 games I need in my collection...

I only picked up a PS2 in November, so I have no doubt missed a few games. Here's what I have :

GTA 3, GTA VC & GTA SA 

Psi-Ops

Shadow of the Colossus

Metal Gear Solid 2 & 3

God of War I & II

Tekken 5

FIFA 07

Onimusha - Dawn of Dreams

Resident Evil 4

Silent Hill 2

Final Fantasy X & XII

Are there any other obvious games that anyone could recommend? From the beginning of the PS2 right to present.

Thank you much!

 Must-have: DMC 1 & 3, Marvel Ultimate Alliance, and a Burnout (Takedown, Revenge or Dominator) game... 

Okami

Bully 

If you like shadow of the Colossus, you have to pick up Ico (it's part 1 of the story)

- The whole Ratchet & Clank series is awesome for platforming;

- Dynasty Warriors is my guilty pleasure (repetitive hack and slash)

- Dragon Quest VII and Kingdom Hearts are other good RPGs

- Maximo if you liked Ghosts & Goblins (it's the 3D sequels)

Classic gaming: Capcom Classics Volume 1 & 2; Mega Man and Mega Man X; Genesis Collection; Street Fighter Collection

PS1 games from Buy.com: The Final Fantasy greatest hits games FF 1 through 9 and the Oddworld games

Sports: Madden is good to pass the time and Tony Hawk Pro Skater 4 is well worth a few bucks from Gamestop.

* I second the recommendations of Bully and the Prince of Persia games.

Definitely pick up a Ratchet & Clank game. They're a good mix of platforming and shooting and have a lot of character. Plus, they're all only 20 bucks (or less).
Devil May Cry 1&3 (the 3-pack is a better deal, but DMC2 is worthless)
Zone of the Enders 2 - if you can find it. By far the best Robot Action Game ever!
ICO - again, if you can find it. It's the spiritual prequel to Shadow of the Colossus

Take Devil May Cry and .Hack//GU

spider-man 3

the new tomb raider

 all the kingdom heart games

all the prince of persia games

ultimate spider-man

Zone of the Enders: The 2nd Runner, Onimusha 3, ICO, Devil May Cry 1 & 3, Ratchet and Clank series, Jak series.

Mega Man Anniversary collection, Mega Man X Collection, Sonic Mega Collection, Street Fighter: Anniversary Edition, Street Fighter Alpha Anthology, Sega Genesis Collection, Capcom Classics vol. 1 and 2 are some great compilations.

You should also get Metal Gear Solid(PS1) to have the whole series.

A layout of must haves for a PS2 (may it never die!)

Kingdom Hearts I & II

Gauntlet: Dark Legacy (great party game if you have a multitap) STAY AWAY FROM SEVEN SORROWS THOUGH IT SUKS

Rogue Galaxy

Drakengard 1 & 2  both amazing games

Disgaea 1 & 2 (only if you have patience and like strategy based rpgs)

Sniper Elite (By far the best FPS you're going to find for the PS2, the AI is amazing and I have yet to see the Axis use the same attack patterns when fighting you...it takes a lot of strategy and hiding out to beat this game)

 I'd also pick up the first dot hack series at least, G.U. is debatable as its for the storyline and it lacks the open ended game play of the first, both series are amazing though.

Shadow Hearts , Covenant, Into the New World (If only one get Into the New World, it side tracks from the first two games and some of the characters are amazing.)

Star Ocean: Until the Ends of Time (AMAZING GAME, a lot like Rogue Galaxy but not as great in graphics)

Valkeryie Profile 2  ...it's a good game and its a 2 player rpg so its worth the buy in my book

 Tales of the Abyss (Great graphics and a 4 way possibilty with multitap)

soul calibar 2 and 3, call of duty 2 and 3, ratchet clank series

dragon quest VIII

ff VII( the remake)

ratchet and clank, all 4 of them 

socom, number 3 or CA

jak and daxter

guitar hero

singstar (highly recommended), pop is better but rocks is also run.

ddr , any ddr you can find 

kingdom hearts

okami

bully

psychonauts

xenosaga

prince of persia