Yes, clover is another favourite of my chickens (I just posted in another thread about dandelions which are also apparently delicious to chicken taste-buds).
My chickens have been really good at choosing what they will and won't eat when given free-run of pasture. They eat lots of grasses, clovers and broad-leaf weeds while avoiding anything in the nightshade family (including tomatoes), castor-oil plants, and marigolds.
I have a book of common weeds in NZ and had a fairly good idea about what weeds would be likely to be toxic to livestock in general and poultry in particular. I think the chickens must have read the same book because their grazing matches up very nicely with what I thought they "should" and "shouldn't" eat.
A word of warning though, if you leave them on the same piece of ground for long enough they will end up eating everything. You're better to move them as soon as they've given the patch the once-over and eaten their first-choice plants.