Everyone has different preferences when it comes to lubricant, so let me start
with what are not good lubricants. Vaseline (and all petroleum-based
products) destroy condoms and tend to be too thick for intercourse. Using food
products (e.g. chocolate or maple syrup) is a very good way to get a yeast
infection. Finally, industrial lubricants (e.g. WD-40) are not formulated for
human use, and I would avoid them.
K-Y Jelly is the old standby and it has the advantage of being available in
almost every drug store. However, a lot of people don't like the taste and
find it to be too thick.
My personal recommendation is AstroGlide. AstroGlide has an
interesting history. It was originally developed as a seal lubricant for NASA
(as in "O-ring seals" not sea lions!). The scientist who invented it
was talking to his mother one day, who mentioned that she was having problems
with post-menopausal dryness. Well, he recommended that she try his new product,
one thing led to another, and now it is one of the top selling sexual
lubricants in the country.
The advantages of AstroGlide (and some of it's competitors like
Probe, I-D, and Slippery Stuff) are that they are
water-based, odorless, tasteless, light, and can be reactivated with water or
saliva. They tend to be more natural feeling than KY and some of the thicker
variations. But, try out several, and see which one works best for you.