It is very unlikely that Samsung will ever release an unmodified Android firmware for the Galaxy S II. They've never released one for their Galaxy S family of phones without their TouchWiz "enhancements".
Historically the only Android devices that have run the stock OS have been the very early phones released by each manufacturer (before they'd written their own customizations) and the Google Nexus series of phones. If you stray away from that you are going to get modified firmwares, interfaces and apps.
One of the big downsides to using a phone that has extensive manufacturer customizations is that this means that they will generally be a lot slower in pushing out updated versions of the Android OS to you. Phones with manufacturer customized OS's are normally updated months after the Nexus devices, if ever. This is because the manufacturers have to do lots of work and testing to re-integrate all of their changes and customizations back into the OS every time the base OS changes. Factor in the fact that phone companies often drag their feet in certifying the updated OS's on their networks and you have a huge set of delays before the updates reach your phone.
The big upsides to a customized OS is that the manufacturer will often add a lot of features that aren't available to stock OS phones, eg Samsung's TouchWiz offered built-in wireless tethering well before it was added to the stock OS in Froyo, both HTC Sense and Samsung TouchWiz add remote phone tracking and wiping features to the phones (in most geographic regions), their media players can generally play more formats, and the interfaces often look "nicer".
Your main option for "clean" firmwares running the stock OS for non-Nexus phones is to use unofficial custom ROMs. Many of these use the stock Android interface and apps, with only minimal changes to either. See these questions for more on custom ROMs: What is the difference between: Rooting, Jailbreak, ROM, Mod, etc, and What is the meaning of “flashing a custom ROM”?
Also see this previous question: Android phones without custom UIs
UPDATE: Since this answer was written one things has changed. In mid-2013 Google started offering "Google Play Edition" phones for sale on the Play Store in certain regions in addition to their own Nexus line of devices. These "Google Play Edition" phones tend to be some of the more popular, higher-end GSM phones and are offered with the plain Android OS with Google Apps, and without any manufacturer or carrier modifications, just like Nexus phones. So far these phones have been getting OS updates much faster than their manufacturer modified brethren.
So far the phones available on there in "Pure Google" versions include the Samsung Galaxy S4, HTC One, LG G Pad 8.3, Sony Z Ultra, and Motorola Moto G.
As these are generally the exact same hardware as their manufacturer branded siblings there are often fairly simple ways to apply these "clean" OSs to branded phones (but do check that you really do have the same hardware, some of these phones have variations with the same name, but different hardware in them, eg they may be available in GSM, CDMA, LTE versions with totally different radio hardware and SoC CPUs).