Earlier, "Scott" wrote:

If one were to design their own
sailplane, which airfoil would be
a good choice for low drag and
fairly low speed...

In addition to what some others have written on this topic:

These days it is getting more and more rare to see a sailplane
developer pull an airfoil straight out of a catalog and use it. Now
that 2D and even 3D airflow analysis software has gotten more common
and more affordable, most developers and designers are using custom
airfoils specifically created for with their objectives in mind.

What we are doing with the HP-24 kit glider wings is pretty common: we
started with a catalog airfoil used on some modern racing ships and
used a 2D analysis package (PANDA, I think) to tweak it slightly.

However, it's not unknown for folks start with a pair of straight
lines from 0,0 to 1,0 and nudge them around until they get the
pressure distribution that they're looking for.

As Gary Osoba else wrote, the wing thickness is generally more of a
structural thing than an aerodynamic concern. More thickness gives you
better stiffness/weight, since the stiffness of a beam is relative to
the cube of its depth - or something thereabouts.

In addition to Gary's good suggestion about the Sailplane
Homebuilder's Association: there's a couple of YahooGroups forums that
are good for topics like the ones you raise. There's glidertech for
design/development issues, and HomeSail for construction issues. Of
course, there's a lot of overlap between the two. You can contact me
via email for subscription info for both.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24