for me, if I don't cvm within the first twenty minutes it ain't going to happen.
Usually it comes down to me, going a certain way that feels really good.
I usually last for an hour. If I decide that I want to cvm that night, I will go really quickly and then go back at her for a half hour until she is very sexually satisfied.
I have a six inch penis (which is about average) and use trojans. I really like the condom variety pack from trojan, which can be picked up from Walmart for $13. I also buy them in bulk of about 36 condom packs of ultra ribbed, which are very snug on myself and cost about $20.
Also try lubricated condoms and there are a good number of thin condoms as well.
Durex is supposed to be another good brand that I haven't tried that much of.
A deeper emotional connection really helps as well. My girlfriend and I have great chemistry which makes the sex unbelievable.
Hope that helped,
comic_relief
EDIT: Don't worry about a handj0b, most girls suck at them. I haven't found a girl that is any good at them yet. Same with all of my friends too.