The title says it all. I would do something with Delaware, but I’m not sure what. Probably divide it, the south to Maryland and the north to Pennsylvania. Can’t think of anything else at the moment.
A recurring and hoary topic for discussion by political/geography junkies, but an idle one. The current state and province boundaries are, in most cases, deeply rooted in history and tradition. Changing them would call for overcoming enormous institutional and social inertia (and, in the U.S., getting the consent of Congress and any states involved).
That said, California could probably stand to be split horizontally into two states. 
Who the hell needs a West Virginia?
Well, those of us who live there kinda like it and would like to keep it around.
The idea that we need TWO Dakotas is ludicrious. One should be enough.
Can we merge Connetticut and Rhode Island into Massechussets?
I also propose splitting both Oregon and Washington along the Cascades, then merging western Oregon and western Washington into one state, and eastern Oregon and western Washington into Idaho.
Northern, Central, and Southern California are no-brainers. We’ll annex Baja California from Mexico while we’re at it and create a new state of Baja. Mexico will keep Tiajuana as an enclave, I don’t want to live in a world where Tiajuana isn’t part of Mexico.
For years now I’ve been pushing for a trade: P.E.I. for Idaho. Economically, both are potato producers, but I’d like to get rid of Anne of Green Gables, and pick up all those fine wild water rivers and natural hot springs.
Can we keep Connecticut and Tijuana, though?
And let’s split Texas up into about five or six pieces just to mess with them. Also I’d split Georgia north of Macon into Upper and Lower Georgia.
Just to buck common thought, I’m going to divide California vertically and call it Inner California and Outer California.
Oh, while we’re at it…the Upper Peninsula doesn’t belong with Michigan. It is clearly part of Wisconsin. The panhandle of Florida should also be sawed off and given to Alabama.
Honestly, you could probably merge the middle of the country into two-three states and Texas, there’s just not enough people there. Hell, Wyoming has half the people of Rhode Island.
Edit: Jophiel, do it along the fault line!
Hey now…them’s fightin words!
{I grew up in ND}
Seriously, though…there should be 2 Dakotas…East and West.
Clearly, the entities that are most in need of being joined are Alberta to Quebec and Texas to Massachusetts. (Their geographic separation would tend to reduce the outright warfare that would result.)
We should make all states equally square. Why let Utah have all the fun?
How about Chali and Cargentina?
A friend from Utica thinks New York City should become it’s own state, taking its NJ and CT suburbs with it as hinterland. Then, New York state and non-NYC NJ and CT would probably be better represented and served in Congress. (I’d also have an annual lottery to choose the mayor, but I digress.)
Will NYC take Long Island with it?
NO! We don’t want it back!
I would make separate states of our largest metropolitan areas, starting with the first eight on this list (from New York to Washington). A metropolitan society and economy needs a government with state-level powers to plan for its needs – and, in particular, to tax the 'burbs to rebuild the blighted inner cities.
Can we take all of the trailer parks here in Florida and call them “Lower Michigan”?
California should be split along a line just below San Jose, and the resulting pieces should be called Superior California and California Centrale, to go along with the Baja part that already exists.
We could trade Mexico straight across baja for texas.