For someone who has only flown a trainer? You're kidding, right?

Something with a reasonably thick airfoil and some dihedral is a typical choice for a second plane. The already recommended Lazy Tiger P-51 ARF fits this bill quite nicely.

A seldom mentioned, but great choice is a Pilot 20S kit. You can see an example of the original version in my gallery. This was my second plane, many years ago, and it flew great. Unfortunately, it only lasted a month. My instructor had a momentary loss of memory and turned on his radio (we were both on orange and white) while I was flying. Plane was totaled. He bought my 3rd kit, the low wing version, which also flew very well. I flew this plane for years before it was just worn out. I highly recommend both versions of this kit.

To see the current version, go here: http://www.modelrec.com/search/pilot.asp and look at the Combo 25S and Combo Wing kits. Pilot kits build well, and pretty easy, the only downside is the instructions are a bit vague. I built my most recent Pilot kit last fall and I was very pleased to see that the quality of cut and fit is still as high as it was years ago.

A great transition to the spacewalker would be to build the S version as a trike and then the L version as a tail dragger.