I've always thought the A Farewell To Kings was a very underrated album that has some of their best writing, and some of the best performances as well.
Of course, the over-the-top and overtly obtuse 2112 is still a classic.
I also like the song Battlescar that, although is a Max Webster song, features Lee and Peart both playing and Lee singing lead and backup, and I think that the composition is Mitchell/Lee if I'm not mistaken, which I am often, so don't hurt me.
Peace,
Pierre