They can get a bit on the metal side, but I am pretty sure the Pink Floyd fan in you will appreciate the musicianship and talent that these guys have. Like others have mentioned, I think Lateralus is their best, mostly because I love Danny's drumming on it. I always shake my head when I think about the wiki entry for the song Schism:
"Schism" is renowned for its use of uncommon time signatures and the frequency of its meter changes. In one analysis of the song, the song alters meter 47 times.[4] The song begins with two bars of 5/4, followed by one bar of 4/4, followed by bars of alternating 5/8 and 7/8, until the first interlude, which consists of alternating bars of 6/8 and 7/8.
The following verse exhibits a similar pattern to the first, alternating bars of 5/8 and 7/8. The next section is bars of 6/4 followed by one bar of 11/8. This takes the song back into alternating 5/8 and 7/8. Another 6/8 and 7/8 section follows, and after this the song goes into repeating 7/8 bars.
The middle section is subsequently introduced, consisting of three bars of 6/8, one bar of 3/8, and one bar of 3/4 repeating several times. At one point it interrupts with two bars of 6/8 followed by a bar of 4/8, twice. A single bar of 4/8 is played before the meter switches back to a set of 6/8 for two bars and 2/4 for one bar. This repeats, setting up another section: two bars of 9/8 followed by a bar of 10/8, that pattern again, and then a single bar of 9/8 followed by a bar of 6/8 and then a bar of 7/8. Next is a set of two bars of 6/8 followed by a bar of 2/8 repeated four times then a single bar of 6/8. The outro has alternating bars of 5/8 and 7/8, ending with alternating 6/8, 2/8 that one could interpret as pulsing with a 4/4 feel.
The band has referred to the time signature as 6.5/8
My 2nd favorite album is Undertow, mostly because that was one of my most played albums in HS. I saw the video for Sober and have been hooked since.
I guess depending on your taste and tolerance for the metal side would be my suggestion for what album after Lateralus to try. My gut feeling is to give 10,000 Days a listen after Lateralus. It's probably more prog than their other 3, but I think it has a great blend of all their sounds. (again, the Floyd fan will love the 17mins+ that is Wings for Marie Parts 1 and 2) Aenima is my least favorite, mostly just due to the interludes irritating me if I am not the mood.