oh and is bitters = Angastora bitters?

Yes.

I always keep Peychaud's bitters as well, they're very good in a Sazerac. Orange bitters are sometimes called for as well, you can get orange bitters here in the States from Fee Brothers - 716-544-9530. Peychaud's and Angostura bitters should be available everywhere spirits are sold.
When you read 'bitters' in a cocktail recipe it's safe to assume they mean Angostura bitters. Otherwise the writer will specify Peychaud's or Orange bitters, etc...

Just to illustrate the difference that bitters/cordials can make, here's an example from the Esquire Drink Database regarding Manhattans:

2 oz good rye (in case of emergency--you need a Manhattan and you're passing a bar of the "Rye? Nah." variety--Canadian Club will do; it's got lots of rye in it)
1 oz Italian vermouth
2 dashes Angostura bitters

Strain into in chilled cocktail glass and garnish with twist or, of course, Maraschino cherry (which is subject to the same challenge re: purity as adding an olive to a Martini).

Of course, human beings, being human beings, can never leave well enough alone. Here, then, are the obligatory variants.

First, a few you can make by monkeying around with the bitters: lose the Angostura and pitch in a splash of Amer Picon and it's a Monahan; a splash of anisette and it's a Naragansett; two dashes of cherry brandy and a dash of absinthe and you've got a McKinley's Delight. Leave a dash of the Angostura in, add a dash of orange bitters and three dashes of absinthe: a Sherman.
Or you can tinker with the vermouth. Replace half the Italian vermouth with French for a so-called Perfect Manhattan. Equal parts of rye, French vermouth and Italian vermouth: a Jumbo. Make that with bourbon: a Honolulu (no bitters at all in those last two). Cut the Italian vermouth entirely and make it half bourbon and half French vermouth: a Rosemary. To turn that into a Brown University, just add a couple dashes orange bitters. Coming almost full circle, if you make your classic two-to-one Manhattan with French vermouth instead of Italian and a dash of Amer Picon and one of Maraschino, you're in Brooklyn. And there are more--the Rob Roy, for one, but we gotta stop somewhere.

If you don't know what Amer Picon is, or the difference between French Vermouth and Italian Vermouth or why it's important...or if you just wish to learn any number of interesting things regarding the cocktail, here are a few good places to delve for answers. Have fun, kids.

Hoy Hoy!

Esquire Food and Drink database

Hotwired Cocktail