In my ideal matter the law firm works on it under a fixed fee, so invoices are simple. Real life, however, mostly serves up hourly bills. Each monthly bill is like a layer in lasagna (See my post of Feb. 21, 2007: standardized formats of bills.). The good stuff (cheese, meat, sauce) should be the narrative at the start about the two or three tasks that took the most time during the month and their approximate cost.
More tasty stuff lies at the bottom of the layer with a table that shows each timekeeper, their billing rate, hours and total amount billed. The recap gives additional flavor (See my post of Sept. 28, 2008: the importance of a recap on an invoice.).
In between is the filler, the minutia of daily time entries, the tangle of pasta.