How much money are you looking to spend. There are a million mods that'll give you long battery life. I'd stay away from the disposable ones. The eGos and the Twist and kGo. The Twist will last all day, but it's disposable and what are you going to use when it's charging? You don't want to charge it overnight while you sleep. Waking up to a burning house is no fun.
You need something that takes an battery from size 16*** to 18***. Not a battery sealed up inside the PV, but a separate rechargeable battery. If you have $85 to spend, go for a Silver Bullet. It will outlive you. There is no tougher, more durable and better built PV on the planet. Altsmoke.com is the oldest approved company on the vendor list, so no worries there.
If $50 is more in your budget, the e-Power I posted the link to takes separate batteries and is pretty durable and reliable too. It looks like a big eGo, but it's not a disposable like the eGo is. It takes 18650 batteries and includes two 2000mah size, which would let you vape for 20 hours straight each.