I use anything I can find: coffee grounds, leaf mould, partially decomposed compost,pine needles, etc. In the veggie garden, I pull the weeds (& if they are seed-free), lay them down on the soil as mulch. Not pretty but it does hold in the moisture and they eventually decompose.
I have a few types available and prefer leaves and pine straw. Very few weeds in pine straw so there is that.
I use homemade compost out of the compost bins for mulching the roses, if i have any left i'll put it around the fruit bushes.
I have not cracked the leaf pile from last fall, nor the sawdust from dead trees cut. I will chip the ramial branches we have collected over the last year to serve as mulch and for mud free walk paths in the garden.
I do not often mulch the flower garden, but I do mulch the veggie plots every year however. If I do mulch the flower garden I do it with compost or composted wood chips from the paths.
@Odif why not cardboard? I have runaway myrtle and pachysandra so I cut them down to the ground, cover with cardboard, then cover with wood chips. It has worked to get rid of the runaway ground covers. Does cardboard just not compost well when in the pile?