Following up on this post, I've made two new maps of proposals to redraw the county borders in Arizona and California. (Update 2010-09-21: I've split California into three maps: North, Central, and South.) It's unlikely to happen in either state, but I think it should be given serious consideration.
When drawing the new borders, I tried to consider (as much as possible given the limited resources I have at my disposal) factors such as physical geography (keeping watersheds intact as much as possible), size, population (at both extremes), and economic interconnections. (In Arizona I also made a few counties that coincide with major reservations so as to eliminate jurisdictional issues.) For instance, in the case of Los Angeles County, it is huge (larger than both RI and DE), heavily populated (it would be the 9th most populous state), and geographically divided (the San Gabriel Mountains range up to 10,000 feet high). I trimmed it down to a more manageable 1,000 sq miles (down from 4,700) and 4,000,000 people (guestimate, down from 10,000,000), all of which are south of the San Gabriel and Santa Monica Mountains.
Because of my limited resources, these maps are diagrammatic. But I think they would be a good starting point for the discussion in each state.