I just ordered from herbiesheadshop.com and I've heard good things about them and you can buy single seeds and get free ones. Nirvanashop.com is good too, just you can't buy single seeds from 'em but my seeds grew beautifully from them as far as I got.
Do some looking around and research to what strain you want, there's so many it's overwhelming for a beginner lol. Don't rush!