A myriad of possibilities
A multitude of options
=> Same meaning, myriad is more literary, multitude is formal.
A heap of coal
A pile of clothes
=> both are untidy, but pile means there are things put on top of other things, whereas a heap a no order whatsoever. Note that you often can use pile in place of heap (eg. a pile of spaghetti/sand), but not conversely: a heap of books (=thrown any old how) doesn't look like a pile of book (=somewhat stacked).