With that in mind, here are a bunch of comics that I no longer have room for. (These are paperback collections rather than monthly issues.) If you'd like any of them, let me know; I'll wait until tomorrow (Thursday) evening, then put whatever's left on Freecycle.
* Black and white reprints
DC Showcase: The Haunted Tank vol 1
DC Showcase: Justice League of America vol 1
Essential Captain America vol 1
Essential Fantastic Four vol 1
Essential Super-Villain Team-Up vol 1
* Strips (mostly black and white)
The Calvin and Hobbes Tenth Anniversary Book
Dilbert: What would Wally do?
Dork Tower vol 1: Dork Covenant
Dork Tower vol 2: Dork Shadows
Dork Tower vol 3: Heart of Dorkness
Dork Tower vol 4: Livin' La Vida Dorka
Dork Tower vol 5: Understanding Gamers
Dork Tower vol 6: 1D6 Degrees of Separation
Dork Tower vol 7: The Dork Side of the Goon
Dork Tower vol 8: Go, Dork, Go!
* Batman and/or Superman
Batman: The Long Halloween
Batman: Dark Victory
Batman: A Death in the Family
Batman: Knightfall, part one: Broken Bat
Batman: Knightfall, part two: Who Rules the Night
Batman: Turning Points
Batman: Arkham Asylum
Batman: I, Joker
Superman: The Odyssey
Superman: The Man of Steel
Superman: They saved Luthor's brain!
The Death of Superman
Superman: The Trial of Superman
Superman: Return to Kryton
Superman/Aliens 2: God War
Superman and Batman vs. Aliens and Predator
100 Bullets: First Shot, Last Call
Angel: The Curse
Ares: God of War
Destiny: A Chronicle of Deaths Foretold
Doctor Spectrum: Full Spectrum
It's a Bird...
Jimmy Olsen: Adventures by Jack Kirby, vol 1
New Warriors: Defiant
Nightwing: Ties That Bind
Puffed: The Unauthorized Movie Adaptation
The Punisher Presents: Barracuda
Robin: A Hero Reborn
Strange: Beginnings & Endings
Thor: The Eternals Saga
The Astounding Wolf-Man vol 1-2
Wonder Man: My Fair Super Hero
X-Factor Visionaries (Peter David), vol 1-4
Ultimate X-Men Ultimate Collection vol 1-2
Ultimate X-Men/Fantastic Four
Zot! vol 2-3
* Misc notes
"Batman: Arkham Asylum" seems to have a good reputation, but I didn't like it; Dave McKean's artwork is just too weird for my tastes.
"It's a Bird..." isn't actually a Superman comic - it's a semi-autobiographical story about a guy who's hired to write a Superman comic, linked in with stuff about Huntingdon's disease. It's sufficiently "worthy" that I'd feel bad for criticising it. However, I'm turfing it out, so draw your own conclusions from that!
"Doctor Spectrum: Full Spectrum" is a spin-off from "Supreme Power"; that in turn was JMS' reboot of "Squadron Supreme", which took a long time to fizzle out without achieving anywhere near as much as the original story (at least while I was reading). This spin-off is by a different writer, and it takes a long time to cover the same ground as part of "Supreme Power".
Speaking of JMS, he wrote "Strange: Beginnings & Endings". This is a reboot of Dr Strange's origin story, so it doesn't really fit into the mainstream Marvel universe, but it's never been followed up on anywhere else. It's a nice enough story on its own merits, though.
The "Calvin and Hobbes" book is good, and it includes comments from Bill Watterson on some of the strips. The only reason I'm ditching this is that I have the hardbacks that reprint all the strips. (Sadly, they don't include the commentary.)
Similarly, the "Zot!" books are excellent, and I'm only ditching them because I have "The Black and White Collection" which effectively reprints vol 2-4.
"Puffed" is an amusing idea (a guy who works in a theme park gets stuck in a dragon costume), but I think it was let down by the execution.
"Infinite Crisis" is one of the worst comics it's ever been my misfortune to read, let alone pay for. However, it's "significant" for reshaping the DC universe (again).
Feel free to ask me for my opinions on any of the other comics, and I'll elaborate in the comments.