kanye west - those slightly unorthadox snare drums (go and listen to encore, jay-z, you'll see what i mean)...
timberland - crazy drum patterns, distinct synth sounds - dont know what he uses, but i recognise a lot of it
neptunes - pharell's `ive got baby nuts` voice, pop hooks
heatmakerz - some sample (typically vocal but any will do - opera samples, sesame street, whatever),
add 1 parts bassline and 6 parts drums, preferably make them loud enough to blow out your speakers, spot em a mile away
dre - hmm used to be distinctive, nice sawtooth bassline westcoast oscillated synth noises etc, but maybe the people he's biting have changed their style now lol?
premo - gotta be the drum patterns baby, along with the way he chops, look at the recent royce 5 9 track `hiphop` - how could that not be premo??
kanye west - well, not actually that easy to spot i think - yes of course youve got the `vocal samples at 45rpm` thing but then hes not limited to that (how does `stand up` ludacris sound like `thru the wire`??)... generally hes dope, i guess
prodigy - ahaaa, hes just evil - take a look at his recent track with Lloyd Banks.... nasty
thats all i can think of for now..