Limiting this list to books I already own (off the top of my head):

Maus - I've owned volume 1 for years, but haven't touched it.

Alice in Sunderland - I've owned a signed copy for ~3 years now, but didn't get past the 1st page

Pogo v1 - I was all excited to get this first volume, and have been anxiously awaiting for it for years, but haven't read it yet.

Little Nemo in Slumberland - I've owned the Evergreen volume and the So Many Splendid Sundays books, but have yet to read more than 3 or 4 strips.

League of Extraordinary Gentlemen - Yes, I've read the comics, but I have NOT read the text stories.

DC vs Avengers - I've owned the Absolute for awhile now, but maybe now is the time to read it with the excitement of the Avengers movie.

And this is a bit of a cheat:
Starman - I read the tpbs, but unsatisfied by the format and the missing issues, so I bought all the back issues and bound them (but never read them since binding the run), and a couple weeks ago, I bought the Omnibus series.



'Reading' / 'Reading soon' stack: DC/Vertigo - ArtOps, Batgirl, Gotham Academy, Gotham by Midnight, Injustice; Marvel - Allred's Silver Surfer; Other - Abe Sapien, Descender, Fight Club 2, Goon, Mind MGMT, Southern Bastards