Well I might as well throw my $0.02 into this...
Wait For Sleep/Learning To Live (I really cannot listen to them separately anymore, nor consider them as such)
Metropolis
Under A Glass Moon
Take The Time
Surrounded
Pull Me Under
Another Day
IAW was one of the first DT albums I had ever heard, and it blew me away. The odd mixture of Rush-like Prog with heavier metal sounds really threw me for a loop at first, but then I began to listen to it more and heard more each time, understanding all the intricacies of the music, especially the longer instrumental breaks and solos, which to this day, still amaze me. "Metropolis" and "Learning To Live" still wow me and I doubt I could ever get tired of those songs. I think it says something to the power of those two songs (and the rest of the songs on the album, really) that the band still plays them today. I mean, how often does a band play music from their 2nd release/an album over 20 years old? When Rush reached their mid-20s, they barely played anything before their 4th album! Not that Fly By Night was their Images And Words, but it really shows how strong their material was on their 2nd album that they can regularly play "Metropolis" and "Learning To Live", as well as "Under A Glass Moon" and "Pull Me Under".
-Marc.