Here's a list of all of the games unlockables.

Clear easy mode:
Gallery unlocked
Total Ranking unlocked
Easy mode screen unlocked in "Clear bonus art"
"Crazy gameplay video" added to Gallery.
Costume: Shirtless Dante.

Clear normal mode:
Gallery unlocked
Total ranking unlocked
"Concept art" unlocked, all pictures visible.
Normal mode screen unlocked in clear bonus art.
Crazy gameplay video
E3 promotional video added to gallery.
Hard mode vailable.
Costume: shirtless dante
Costume devil may cry dante

Clear normal mode with s rank in all missions:
Normal mode s rank clear screen unlocked in clear bonus art.

Clear normal mode with perfect (ss) rank in all missions:
normal mode perfect rank clear screen unlocked in clear bonus art.

Clear hard mode:
CG art unlocked, all pictures visible.
Hazuma Haneko's illustrations unlocked, all pictures visible.
Hard mode screen unlocked in clear bonus art.
"Video storyboard" added to gallery
Costume: Devil May Cry shirtless Dante, Lady alternate costume
Dante must die mode available

Clear hard mode with s rank in all missions:
hard mode s rank screen unlocked in clear bonus art.

Clear hard mode with perfect (ss) rank in all missions:
hard mode perfect rank clear screen unlocked in clear bonus art.

Clear Dante must die mode:
Dante must die mode screen unlocked in clear bonus art
Costume: Super Dante, Lady alternate costume.
Heaven or hell mode available.

Clear DMD mode with s rank in all missions:
DMD mode s rank clear screen unlocked in clear bonus art.

Clear DMD mode with perfect (ss) rank in all missions:
DMD mode perfect rank clear screen art unlocked in clear bonus art.

quote Spoiler

Vergil special ending:
To view the Vergil special ending, you must kill 100 enemies during the credits at the end of the game. The 100th enemy is a Hell- vangaurd.

um about the extra ending part what do u mean by kill 100 enemies..? do u fight them wiff unlimited heath or something..or is there a time limit..?

Don't know, havenet gotten there yet, i'm only on mission 13. I got these out of the back of my limited editon guide.

quote Spoiler

There's also a Sparda costume, but i'm not sure how to unlock it. With the sparda, devil may cry dante,and dmc dante shirtless when you Dt you become spardas DT.

all these can be found on the guides on the neoseeker forums.

just do a search for devil may cry 3 faq/guides, there is an indepth description and walkthrough of everything you need to know about dmc3

here is the link:
http://www.neoseeker.com/Games/Products/PS2/devil_may_cry_3/faqs.html

the sparda costume is great You get it buy i guess beating HOH but I just used the cheat to get it hahaha, it looks like Virgil yet in like midevil noble garbs and he has only 1 eye and the DT is exactly like the one we see in the begging of DMC 1. but Lady alternate costumes? she isn't playable and I haven't found a way to change her cloths.

Yaw! i was gonna ask that too how the hell do u change lady's costume?! is it like based on what costume ur using will cause hers to be different or something? i dont get it? and doesnt superdante or w/e have infinite devil trigger?

Her costume changes during the fight against her in mission 16.

ummm which costume is it that gives Dante inf. DT ?

ummm one more thing just wondering....I i use the " Unlock everyting code" does it ruin my previous game casue it says to do it on the main menu screen can i just start a new game...? and will it still effect my old game..has anyone else tired this..yet..?

It doesnt affect your game it appears as though you have every costume and every difficulty.

yea but if i just wanted to see what its like can i check but without saving can i still keep my original game...w/o extra thigns the cheat gives...gave me

like lets say i try the cheat i test all the gizmos then im done can i shut off the ps2 and then return to my game and would it still be there..i kno that an obvious answer..but hear me out and how would i bea able to change costumes...like is there a special screen? cause i wann try the co-op story mode with Inf.DT by wearing Super Dante and the dopleganger trick sounds very..fun...can any just give me step i would/should take would very helpful. thx in advance

Transfer your file to a different memory card, pop the new card in and enter the cheat. Then go back to your other card when you want to use your un-cheated file.

It's a shame that the DMC2 costume wasn't included as an unlockable. Granted, Capcom probably doesn't want to remind anyone of that disaster of a game, but the costume was indeed very dapper. I would've liked to see it brought back.

Yeah, you make a good point. I mean, they've gone to the trouble of including all these other costumes, so while you're at it why not add a costume for which the model is already done and all you have to do is import it from your DMC2 data at Capcom HQ (or wherever) to DMC3? Though I've personally never found alternate costumes that appealing as they're only cosmetic and don't usually affect the gameplay in any way.

Hey JG, long time no see buddy ! I also quite liked Dante's standard attire from DMC2, though I think his DMC1 look suits his (non-DMC2ed) attitude more, I still thought the costume from 2 was neat , shame they left it out...

Dman, are you avoiding me ? I can't believe the Modernerator is avoiding me ...