It is more than a year now people are expressing their exchange of choice. So, I thought of listing them below...
Direct Trading Exchange :-
i. www.LocalBitcoins.com
Real Time Exchange :-
i. www.BTC-e.com
ii. www.BitStamp.net
iii. www.Kraken.com
iv. www.CoinBase.com
v. www.OKcoin.com
vi. www.BTCchina.com
vii. www.Cryptsy.com
viii. www.Bitfinex.com
ix. www.Bit-X.com
x. www.huobi.com
personally, i use only btc-e , it was first exchange site that i ever used and i just like this, i like it's design , and this exchange site don't have bad reviews about it so i like to use it
but also, there is exchange site named bitstamp and most of my friends use it and describes it as best exchange site, so i think that they both are pretty good, you should check them out