Okay this sounds easy....not

Buffy :-

One-Off - Probably a random monster/vampire but only because I can't think of a more interesting character off-hand

Recurring - Willi the bartender..Cool job and he gets some cool lines "Have you two girls ever done modelling, cos I've got a friend with a camera..."

Regular - I was going to say angel for the good looks and mysterious personality but I've chosen Xander for the comedy element.

Angel :-

One-Off - Was gonna go random monster/demon thing again and then I remembered the Vampire in the episode where Spike is searching for the Ring of Amarra(? - something like that) from series 1....he seemed pretty interesting

Recurring - Either Lorne or Lyndsay...karaoke rocks and I wanted to be a lawyer when I was younger.

Regular - Angel even though it would ruin my tanning oppurtunities

ER :-

One-Off - A patient who dies after commiting some really heroic act(wanna look brave and cool )

Recurring - Jerry from the desk. Not sure if he is a recurring but Mmmmmm donuts

Regular - Carter cos he's seen it all now

ok

Buffy
A one off character-random vamp!
a recuring character (who isnt in the credits)don't know!
a series regular (who is/was in the credits) Willow

Angel
A one off character-random vamp
a recuring character (who isnt in the credits) Darla
a series regular (who is/was in the credits) Fred/Cordy

ER
A one off character-random patient
a recuring character (who isnt in the credits)that receptionist lady.
a series regular (who is/was in the credits) Abby

Dawson's Creek
A one off character-random extra.
a recuring character (who isnt in the credits) Gretchen
a series regular (who is/was in the credits) Jen

forgot a couple!

Roswell:
A one off character-waitress in the Crashdown
a recuring character (who isnt in the credits) don't know!
a series regular (who is/was in the credits) Maria

Alias:
A one off character-random extra
a recuring character (who isnt in the credits)that KGB spy
a series regular (who is/was in the credits) Sydney

Buffy
A one off character - Dracula, to be in the cheesiest episode ever made!
a recuring character (who isnt in the credits) - Jenny Calendar - ok, killed by Angelus, but Giles Smoochies
a series regular (who is/was in the credits) - Spike up to and including season 4, after that Willow.

Angel
One off character - Faith, she got to beat up slimy lawyer guy and end up cuddling Angel (and then prison, but still...)
Recuring character - Lorne, now I just need to learn to sing...
Regular - Cordelia, getting called 'Princess' all day first by Glenn Quinn and then by Mark Lutz...

Andromeda
One Off - Elssbett Mossadim, the kick-ass Nietzschean Sabra First Daughter who ended up marrying Charlemagne Bolivar (who was incidentally played by James Marsters)
Recurring - Freya of the Orca Pride - Tyr's wife. MMmmmmmmmTyr...
Regular - Rommie - as an AI and as the hologram she has access to all the crew's quarters. Even when they've just walked out of the shower.

Buffy -

One off: The Judge, I wanna be a big bad
Recurring: The Mayor, he has power, wealth and an understanding of the need for cleanliness. My hero
Regular: Oz, with his no nonesense coolness

ER -

One off: Paul Sobriki, cos he killed Lucy and acted as a major cataylst in the series, even though he was in it once.
Recurring: Bishop Stuart, what an amazing and sad story to be a part of
Regular: Kerry Weaver, I'd get a cane to hit people with

West Wing -

One off: Senator Stockhouse, described as the president as a "horse's petute"
Recurring: Oliver Babish, the best dame lawyer in the world
Regular: Josh, for moments with Donna

ok, this is really difficult.

Buffy:

One off - i have no idea. i can't think of anyone decent.
Recuring - Proably choose Harmony cause she's just so ditzy. and she had minions!!
Regular - Definitely Anya. She gets all the best lines.

Angel:
One off - the Sister Oracle from season one. she looked really cool with all the gold and blue.
Recuring - Lilah. she's evil.
Regular - Fred. she's insane.

ER:

One off - that weird psychic woman from the season 5 finale who just could tell stuff about people and knew that Carol was pregnant. she was fun.
Recuring - i'd probably go with Chuny.
Regular - Abby coz one word - Carter.

Here goes
Buffy:
one off-
reocuring-Faith, girl gets all the fun!
regular-Tara, she was soo sweet

Angel:
one off - Bethany, the telekinetic, was great. wish i had her gift sometimes.
reocuring-sister Oracle, dressed as her for a fancy dress,cos she was cool. Or Darla, cos she was such a evil sexy lady, and she got to do the nasty with Angel!
regular-Ms evil Lawyer chick, Lilah.

Farscape
one off- PK barbie, Scorpius's red headed dominatrix assistant.Or Natyri, the blue spider lady, cos her make up was incredible
reocurring-captain cleavage, dont know her character's name yet but she's the new insane military commander after Chriton.
regular-Aeryn, cos she gets to wear leather and some times John Chriton!!

Stargate
one off-One of those futuristic aliens that could walk through walls and stuff.
reocurring-Osiris, for a gender confused Gou'ld, shes got a great dress sense, and i wana play with one of their hand devices, cos their cool!
regular-not a big choice hear but i would go for Doctor Fraiser, but i would demand she gets out more!!!

OK, appologies if I list any regular characters as recurring. I just never actually read the credits:

Buffy-
One-Off: Dracula. Not that I could carry it off, but how cool would that be?
Recurring: Oz. Sorry, it's just that I like thinging about Seth Green, not that I particularly want to be his character...
Regular: Xanda. Cos he's sooooo me.

Friends-
One-Off: Joey's ex-boyfriend. I don't think this needs explanation...
Recurring: Richard. You get to smoke. You get to drink. And you get to <edit> monica. What more do you want?
Regular: Chandler. Cos he's sooooo me.

Star Trek: Next Generation-
One-Off: a Klingon. Any Klingon. With a Bat'Leth. And preferably a mating sequence after a good battle...
Recurring: Q. Just because I wouldn't be as iratating as John de Lancie.
Regular: Data. Because he gets to <edit> Lt Yar...

South Park-
One-Off: The undertakers from the Korn episode. They were soooo cool!
Recurring: Tweek. All that caffeine... Mmmmmmmmmmmm
Regular: Cartman. Cos he kicks ass!