you can use coinbase or bitstamp for buying through bank deposit,or use BTC-e but wiretransfer deposit may take some time
where are you from, so we can suggest you best exchange based in your country
I am from India (MP) one thing more i asked this question so that i can instantly buy btc when its rate is luw an instantly sell it when its value rises
and i dont want to sell or buy my btc with any person i just want any website or app that does it.