The most used attachment for mine now is the forks, followed by the smooth edge bucket then the toothed bucket and the land plane. We have lots of rocks so the Grapple rake comes in handy for quickly sifting out the rocks larger than about 6" and the land plane takes care of the smaller ones.
I bought my machine from a dealer when I needed to make a pad for my work shop to be built on. It came with the toothed bucket and I have used it enough to put about a 1/2" deep eyebrow on the edge of the bucket between the teeth while cutting the pad (40' x 100') out of the side of a hill in virgin DG, tough stuff for sure.
I was just given an auger, a trencher and a 910 backhoe attachment. The 910 is larger than what was intended to go on the machine (I need to fab a custom attachment plate for it) and all 3 need to have some hoses that need to be replaced and the ends of the hoses changed to fit the flat face connectors of my machine. The trencher needs to have the motor resealed as it leaks a bit but for the money (just come and haul it away) I think it was a good deal.
The more you have the machine, the more you will find to do with it.
Enjoy!