Who I think should be in :
Khmer empire. They dominated a sizeable chunk of south-east asia for quite a few centuries, and left being a number of wondrous constructions (all the Angkor (Wat and co) for starters).
Majarpahit civilization - controled for a long while the islands of South East Asia. Left behind such wonders of the world as Boro-Budur (sp?). They were a major regional power for quite a number of centuries, along with the Khmers.
Mayans. They lasted quite a long time, and left behind impressive traces, such as Chichen Itza. They were also generaly speaking far more "civilized" Than the Aztecs who came after (pinacle of war as capture, not killing ; human sacrifice only appeared very late under impulse from another group who had conquered them). They also were far larger generally speaking than the Aztec (who controled a larger territory, but through submited tribes and military power, not through simply building up their empire...when you get right down to it, the REAL Aztec civilization was Tenoctithlan (admitedly, very impressive in itself) and its armies.
Inca - Another power worth noting. Rich - more than rich, sickeningly rich - and left behind the impressive mountain stronghold of Machu Pichu. They also developed their own system of data transmission which has never been deciphered - the fabled Qipu, built a respectable system of roads in mountain territories...
Spain - The reasons are obvious and already outlined.
Portugal - Same as spain. They kicked forward the great exploration movement. Gama, the conquest of an empire englobing at its greatest Brazil and islands in the South pacific...
Dutch - The third of the five original great exploring countries. Only France and England were in the original, and only Spain is being added - Portugal and Holland should really be in. I mean, there's a reason why all those places Japan was interested into are called "Indes NÉÉRLANDAISES" - "Dutch Indies".
Arabs - Massively contributed to world science through the "dark" ages. All "political correctness" put aside, their contribution to the world is generaly speaking more noticeable where it counts than that of Israel. Certainly, Jews scientist contributed much in later times - but they contributed as part of the countries they had moved to (Einstein in Europe then in the US of A, etc), not as part of any Jewish civilization. Whereas the advancements of mathematics and other such through the dark age is largely credited (with good reason) to the arabs. The size of the Moorish/Arab empire at its greatest extent (most of Spain, north Africa, the holy land...). They *HAVE* done more than the Hebrew civilization for the world, given that most accomplishment by Hebrews were done while they were part of other civs covered already in the game.
Turks - The other half of the muslim menace. Another group which had a great empire, and at one point stood poised to take much of Europe, only being narrowly staved off at Lepanto and such, and in the Balkan by various, including a certain Vlad we all know and love

. They also brought down the Byzantine Empire, and at their greatest extent they, too, controled a vast territory under the guise of the Ottoman empire in the 19th century.
Regarding the Israeli matter, while they are a powerful regional power at present, being a twentieth century regional power does not qualify. Heck, being a Twentieth century *WORLD* power does not qualify, according to quite a few here.
If you consider what ARCHAEOLOGY and HISTORY tell us of Israel (not what the Bible has to say, since it has proven its historical inaccuracy more than once...would it only be with self-contradictions).
What are the great things Israel and Hebrews truely left behind for us to find?
The port of Cesarea. Built by a half-hebrew (at best) ruler who had his throne under the blessing of Rome, named after Caesar Augustus, with a temple dedicated to him in the middle of it, with a status of *ZEUS* in the middle of said temple. Something tell me this would be more at home under a roman civilization, for some (very) odd reason.
The palace of Jericho. Built by the same guy as above, same restrictions applies.
The temple of Jerusalem (the alleged second one, since absolutely no traces of the first have ever been found, and it's been proven that Jerusalem was a very small town at the time of David and Solomon). Built again by the same ruler, in an attempt to make himself popular. One may note that at the same time he rebuilt the nearly palace of the Asmonean kings and named it Antonia - after the OTHER pretender to the Roman throne. And once he died the Antonia became a roman fortress from which to control Jerusalem.
The Fotress of Massada? Built under the same king...
The Herodion? Same king, yet again.
The one major thing the Hebrew themselves (and not an half-greek, Roman-bootlicking king of theirs) left behind is a strong monotheism. Now that could be considered basis enough for inclusion as a civilization, but frankly I simply happen to think there are a swarms of other groups more worthy of the role than the Hebrews. And to be fair, most of the great lines of the Jewish faith were written down in the Torah...during the exile in Babylon

.
While it is true that further down the line jews contributed much to human history, these contributions were brought in as part of whichever civilizations they happened to be with at that particular time. IE, under the romans, or under whatever group they were with.