As far as longest battery time is concerned, Lenovo Rocks, Absolutely no question about its capabilities. I've got Lenovo R61 8920 and with a 6-Cell battery, the usage time is around 5 hours (casual usage) and around 4 hours running power hungry applications.
I also own an HP dv6059EA (6 Cell battery), I purchased it about 2 yrs back, at that time the battery life was around 2 hours and now its around 1 hr and 15-20 minutes. Here I must mention that its an entertainment notebook with lot of multimedia buttons (shashkay ).
If you ask me, I'll select Lenovo without any hesitation.
Technology is advancing quite quickly, you can find a laptop with handsome specs, quite cheaply.... If you want to live on the edge, check a lappy with 250/320GB Hard disk (preferably 7200RPM) equipped with DDR3 RAM, intel C2D processor etc.