I am thinking to buy a lens for my sony a330.Right now it has 3.5-5.6/18-55SAM..i m just wondering what kind of lens should i go for?Any suggestion will b highly appreciated!!!!!

ANYBODY?????

 well, first u need to be surE what kind oh photography u most intrested in. moreover money u have allocated. there are lens from 200$ to 20000$.

It is for my personal interest!!range from 200 to 500$

 pesonal interest? peRsonal interest in what? taking good pictures of peeps around you, wildlife or taking tiny insects? you need to be specific. if you just want to have an alternate lens to your kit lens, then prime lens ( with fixed focal length with higher aperture ) would be good choice which are cheaper and takes sharper picture compared to standard kit lens.
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 buy a 55-200mm lens. It is usually good to get 18-200mm then u don;t need to carry two lens while traveling. Or getting a 18-135mm lens is also good . This way u can shoot potraits which are good at 80mm as well as some sports photography  @ 135 mm.
I would say first choice 18-200 or 18-300mm
then 18-135mm
otherwise 55-200mm
One thing is get with vibration reduction vibration reduction lets you shoot with 4 times slow shutter speed than comparable.
In addition I think buying a flash is also good , external flash with bouncing lights really enhaches your subject and particularly good for portrait.