I would say that Cosmic Encounter is primarily a game of middle-game, since every time the endgame approaches, players gang up to take the player in the lead back down to the middle. It is usually won by the player who manages to sneak by when people aren't looking, the player who happens to be able to withstand the might of the others combined, or, most often, by several players working together against the others. (I have actually even been part of games where everyone won...

As for games not on your list...

Outpost: This is a game with a definite beginning game (building up some factories and buying the first few improvements), but where the majority of the game is determined by the middle game. Who gets the Outposts, the Robots, and the Laboratories/Scientists really determines the winner, and the endgame is usually (though not always) a foregone conclusion. (Note that it will take you forever and a day to actually find a copy of this game if you don't already own it...)

Kremlin: This is a game with a lot of focus on the middle game. Early on, everyone is trying to play conservatively, not revealing too much about who they've dumped their influence on, but in a couple of turns comes the important points, where you really need to decide what to reveal, what to keep secret, and which members are lost causes, and should be given up on rather than trying to spend points on other guys to try to bring them back from Siberia... :-)

Britannia: This isn't really in the same class of games as the other ones you listed, but it's one of my favorites, and is balanced well in terms of play at various points in the game. Since each player gets new nations at various points in the game, there aren't any overall lulls in the game. Note that individual players can have lulls, though. (Particularly Purple; if the Scots and the Romano-Brits die out quickly, Purple can conceivably spend 4 full turns with nobody on the board at all, but this usually doesn't happen...)

Also in a different class of games is Iron Dragon, a Mayfair crayon rail game. This is the only rail game I've played, so I don't know if it holds true for all rail games or just this particular one, but this is a game with a definite focus on the middle-game. In the beginning, nobody has any money, and is just trying to make their first delivery or two, and by the end, it's just a matter of who got their rails done first, and picked some good load cards to make that final sprint for cash. It's the middle game, especially when one has to work out paths using other people's rails (but trying to minimize that usage), that the real meat of the game is.