Any class with a strong dmg output combined with either survivability or COMPETENT heals can be a great solo class depending how its played.
Also depends what you plan on soloing.
For example K/P has low dmg output and great suvivability but if you dont need much dmg than you are fine... Lot of classes like this, there are just so many factors to consider for what each person wants to do in the game, and they all lead to your perfect class combo
Good all round solo classes would be:
Wl/Ch
M/P
R/Wd
Wd/anything
(usually its warrior/scout/druid secondaries for warden)
Champ has some good options too.
Like I said, depends what you want to solo.