Deere 440's series a b c all good machines depending on how much abuse they have gotten.
Timberjack in the 200's i.e. 206 210 etc
Clark 664 or 666, though the 666 is more of a midsize skidder, and 664's are rare.
Garrett,CanCar,Treefarmer all about the same (all licensed from garrett) garrett 10-15-16 or 21's CanCar/Treefarmer C4 or C5
There are a few more out there, but more rare, Masey Furgeson, and Case both made skidders, Pettibone (If I remember they are the continuation of Treefarmer/Garrett)
If you plan on going with a small skidder then your pretty much looking at line skidders I.E. winch and chokers, putting a grapple on a smaller machine can be done, but its really not meant for it and will increase the center of gravity to absurd levels.
On the same note if you wan't a new skidder first they are stupid expensive and second no one makes a small one, Third they pretty much all come with grapples now. (If you do plan on buying new, can I have 20k its for a good cause...)