Can't go wrong with Why?.

I suppose Subtle's another pretty good hip-hop-that-isn't-really-hip-hop-but-is-it-oh-god outfit.

new album 'April' is great

Everyone should own this record.

Singer/Songwriter.
Totally awesome lyricist.
Sings with an Australian accent which you may or may not like.

(not THE Whip). US folk singer-songwriter. Very good.

I haven't really been a big fan up until recently. You have to listen to 'The Matter (of our discussion)' with Nina Nastacia, it's one of the most beautiful songs I have heard in a long time.

Held By Hands

for some kinda Jazz there last two albums are realy good and Live they are amazing. They rock so hard for a band with no guitar.

Why? Alopecia is really good it aint very hiphopy mind... well I guess the vocals can be some times.

Australian folk pop that sounds all pixie-esque (the magical creature, not the band).

http://www.myspace.com/kesband

No one likes this album but me.

Singer/Songwriter... but has more of an interesting twist if u will may keep you more interested.

Check out Fleet Foxes for a poppier outlook on a folky sound which may also key you to like folkier sounds. I always think listening to bands with elements of certain gernes your unfamiliar with as the best way to get into a genere.

from a singer songwriter point of view you could do worse than Polly Mackey, she is from Wrexham, North Wales and for a 16 year old I think she is pretty special. '18 Hours' is my personal fav;

http://www.myspace.com/pollymackey

Hip-hop - Blackalicious or Saul Williams...very clever stuff.

Singer/songwriter things - Decemberists or Iron and Wine are both great.

Are amazing.

Folk: Jim Moray - takes you use of electronica what you like and plasters it all over traditional English folk songs. The results are quite damn special.

'ma fleur' by the cinematic orchestra. not only is it excellent, but it sits quite nicely inbetween jazz and hip-hop. kind of. think a slightly less sombre portishead.

try Iron & Wine for some folk. Also give Espers a listen for a twist on folk.

Jazz:

Any ECM artist (ECM was a great 70's jazz label), Airto, Lionel Hampton, Jimmy Smith, Dave Brubek, Gil Evans, Early Quincy Jones, Miles, Jean-Pierre Rampal

Folk:

Don't know much about folk but these artists are singer-songwriters with a folk flavor:

Early Dylan

Palace Brothers (Will Oldham)

Nick Drake

Devandra Banhart

More Singer-Songwriters:

Bill Callahan (smog)

Anton Newcombe (Brian Jonestown Massacre)

Daniel Johnston

Roky Erickson

Nick Cave

Micheal Gira (Swans, Angels of Light)

electronic: squarepusher
jazz - jaga jazzist

Check out the album Silent Movie by Quiet Village.

which said if you listen to post rock it's important to listen to Edith Frost, that probably isn't true but she does make some awesome alt folk.

Also the battle of land and sea for more mazzy star esque folk music.

GZA - Liquid Swords
Miles Davis - In A Silent Way (as a good introduction)
Anything sung Luke Kelly for folk music. Or Steve Earle.

it's probably best to look for things which have parallels with your general tastes. On that note (and having looked at your profile), i recommend The Mahavishnu Orchestra

Visceral stadium jazz-rock fusion with incredible musicianship, a cerebral mathy slant and a highly bombastic attitude. Either of the first 2 albums are superb

but certainly have a folk-y slant:
Bowerbirds
Grizzly Bear
Beach House
The Dodos
Bon Iver
Blackbright Morning Light

Hip-hop:
stuff on Anticon and Lex: Why?, Hymie's Basement, Themselves, cLOUDDEAD, Fog, Subtle, Alias, Sole.

Singer Songwriter - Micah P Hinson
Folk - Rachel Unthank and the Winterset, she from the north east amazing voice
Hip Hop - Definitely Saul Williams' send album

You should also give Dan Le Sac and Scroobius Pip a listen bit of electronic hip hop crossover not really hip hop but sort of.

check out this label some nice electronica aswell as a hawk and a hacksaw which is some rather nice apalation folk stuff

Narcosis, R Kelly, Mark kozelek - Little Drummer Boy, Bonnie Prince Billy.

covers your hip-hop, your folk and your singer-songwriter in one. And is awesome. Get Talkin' Honky Blues as a start, maybe?

Probably not... but Tri-State by Above and Beyond is pretty cool

Josh Ritter. I see you're a Modest Mouse fan...he's pretty into them and at live shows often slips bits of MM songs into his own ones, and does a nice cover of Blame It On The Tetons.

If you only listen to one song, listen to "Thin Blue Flame". Not as folky as his other stuff, but (i know i keep going on about it in various threads but) it really is probably the most incredible song I have heard this century. It is...incredible.

....also try out an album called "Cold House" by Hood, as Why? has worked with them. Lovely slice of ambient electronica with hints of post rock and guitars too. Wins all round.