miso wrote:

I'm inclined to go with the Su-27, but for a different reason. Excuse
the lack of technical jargon in this argument, but the SU27 has part
of the body of the plane protruding between the engines, and this
appears to show up in some of the photos (especially the one of the
far right).

I considered that the tail stinger might be showing up in that photo, but I didn't consider the photo definite enough to say
it was there.  The other features are more than enough to idea it, taken altogether.  Like a stretch DC-8, the aircraft has
a distinct gestalt, and seen from the appropriate angle you can ID it from very long ranges, even in a fuzzy photo like
these.

That said, I took the FA18 and the SU27 VRML models from the fas.org
website and attempted to position them like the plane in the 4th
photo. The distance from the end of the canopy to the start of the
wings seems longer in the mystery plane than either the FA18 or SU27.
Here is the image:

VRML:
http://www.lazygranch.com/images/misc/fa18su27.jpg
mystery plane:
http://www.lazygranch.com/images/misc/whitebird2.jpg

The mystery plane seems to have stubbier (sp) wings.

Using angular computer-generated solid-color models with no shadowing to compare with the much more subtly-curved,
variable-color real thing with variable lightingisn't going to prove much:  try comparing photos of the real a/c in flight.
Here's some of a Ukrainian a/c at an airshow, plus a Russian a/c:

http://www.airliners.net/search/photo.search?aircraft_genericsearch=Sukhoi%20Su-27%20Flanker&distinct_entry=true

I don't know if this is a standard paint job or an airshow special.

Guy