there's something to be said about the fact that there are probably three or four bass lines by both Geddy and Steve that laymen hum or sing, and I'm not sure I can name one from JMX. That's not a slight by any means (it's also a function of the bands and the type of music each plays), but it's a variable, at least for me. I'll often find myself humming that bass part in the bridge-ish section of Number Of The Beast.
When I think of Harris, I think of the gallop rhythm that's probably most notable in songs like Run to the Hills and Trooper, but I wouldn't call either particularly memorable. Harris's memorable stuff shows up in songs like Phantom of the Opera (the triplet section in the middle of the song's instrumental), Wrathchild (intro), RttH (the part high on the neck after the guitar solos), To Tame a Land (the 3/4 part around 4:08), etc. For the most part, one song per album.
For me, Lee has innumerable memorable lines, and I think that's mostly due to Rush's style and the fact that the bass is virtually a co-lead instrument with the guitar.
For Myung, it's somewhere in between the two (definitely more than one song per album, but not nearly as ubiquitous as Lee): Ytse Jam (the main riff that's obviously done with the guitar and keys and the solo), Metropolis (solo), Learning to Live (the riff under the first verse and the "Wait for Sleep" section right before the guitar and key solos), the intros to Voices, Lifting Shadows and Scarred on Awake, the intro to New Millennium (although that's done on the Stick), Home and TDOE, the intros to The Glass Prison, As I Am and Panic Attack, etc.
I don't know if any or all of those are necessarily hummable, but I can assure you that pretty much all of them are fun to play.
If I had never SEEN JM perform, I would have no idea, honestly. I think DT's mixes have more or less hidden him big time. His bass really doesn't stand out. I mean, to cite the beginning of As I Am is case in point. It shows how little his stand alone moments are.
Without getting into "stand along" versus "stand out" (and I can think of lots of both), I mostly agree with this, and it goes back to day 1 for me. When I saw DT for the first time (Nov. 1992), I was amazed when I saw all the things that JM was doing that I hadn't heard on I&W. To this day, one of the most enjoyable parts of any DT show is watching to see what crazy things JM is doing that I didn't catch from listening to the latest album.
And yes, JM gets buried big time. That's a product of a couple things (IMO). First, in both live situations and in the studio, he uses a fair amount of distortion. Second, many/most of the songs on the last few albums (not including TA) feature very low-end riffing (i.e., lots of stuff that is mostly or exclusively played on the low B string).
When have you ever heard distorted harmonics on base to start a song before?
That alone makes it stand out.
Not that more than maybe a dozen people ever heard it, but I did exactly that on a song written back in 1990 or 91.