I recommend buying TheyFit condoms. You can get exactly the perfect size for your penis. They are good quality and not a bad price.
Go to:
http://secure.condomania.com/TheyFit/
Make sure to print out a size chart and measure yourself accurately. While we all like to boast about our size, this is not the time to inflate your measurements.
Trust me, you won't regreat getting these condoms.