generally the blue snowball is a good budget choice at $45usd though prices may vary in different countries. uk typically has much higher prices than elsewhere. its a cardioid mic so picks up what you point it at and likes to ignore sources you dont point it at.
as mentioned above if you did not mind a 3.5mm mic, the modmic is a great option if you would prefer hooking up a boom mic to an existing pair of headphones.