It's hard to make a suggestion in the "other" category without knowing specifically what guns you already own, what your interests are and where they might lie, etc. But I'd recommend, if you don't already have one, a Walther PPK -- and one made in Germany, not a USA version from Interarms or S&W. Few guns' designs have held up as well through the years, few guns look as elegant, few guns have that "cool" factor that the PPK has in spades.
Of course, if you've already got one, then go for a P.38 instead -- for the same reasons.