My favorite is the green synthetic grease made by Lucas Oil and sold in tubes for a small grease gun. The consistency seems just right for bicycle bearings and it tends to resist "washing out" when used alongside oil lubrication (e.g., a three speed rear hub or an "oiler port" front hub). The grease is made for machine tools and farm machines/implements that see many more RPMs than even the bottom bracket or the pedals of a bicycle.
Prior to using the synthetic, I used plain, brown household lithium grease, which also worked just fine. The difference was that the synthetic tended to seal-in light oil much better than the lithium (the lithium tended to wash out when mixed with 20 weight machine oil). I think the consistency of the Lucas green synthetic is a little better for the bicycle bearings.
"Bicycle grease" (usually the red/pink Phil Wood stuff) works great as well, but isn't necessary for conventional/old style bike bearings.
"High temp grease" usually isn't necessary. If you're really jamming on a coaster brake and cooking normal grease (like the re-pack run guys used to do) high-temp grease is probably needed. But if you're just conventionally riding, the high-temp isn't needed. Use the high-temp on your coaster brake if you want, but hopefully you're not riding the brake so much that you're cooking off grease (and killing antique coaster brakes while you're at it).
There is no "magic grease" that's better than everything else and that will make your bearings last forever, contrary to what the advertisers tell you. What keeps your bearings, cups, and cones running properly is maintenance and cleaning. Keep some grease, oil, and cleaning supplies in the garage and know what the bike should feel like when it's running well. Don't keep riding a bike when something starts to feel dirty, gritty, or just plain off.
