As a fellow Marvel-centric, the only DC I can recommend are the classics you have already read - Alan Moore. If you havn't, V for Vendetta, Watchmen, League of Extraordinary Gentlemen are all classics - and Moore's take on regular DC heroes like Batman, Superman, etc. are great too.
(I'm not sure if all of Moore's work I described is DC, but still check it out)
If you like Marvel, you probably like the darker, grittier, stuff. As such, I would recomend anything Batman. Except for all star Batman ad Robin. Or the Dark Knight Strikes again. Those freaking sucked. But Hush is one of my favorites. Avoid Countdown to Infinite Crisis.
The only thing I like about Marvel is their older stuff before they were all about marketing. The only thing I know about Image comics is that it involves Liefeld. The only thing I know about Liefeld is that Linkara of That Guy with the Glasses fame says to stay away from anything Liefeld related. But then again I can't just go on the word of someone I have never met, maybe I will look into Image.
Liefeld had a falling out with Image some years back. The big names in Image at the moment are Todd Macfarlane (Spawn), Jim Lee (the dude who was the artist for Batman: Hush (on topic, read Batman: Hush. it rocks)), Marc Silvestri (Witchblade, The Darkness, founder of Top Cow Productions), Eric Larsen (Savage Dragon), and the newest addition to Image's lineup of partners (not to mention the first addition to their partners since the foundation of the company) Robert Kirkman (Walking Dead, Invincible, Astounding Wolf-Man, Haunt, Brit, Image United, And Battle Pope).
I strongly suggest Invincible and The Walking Dead. Both are so good. Spawn and Witchblade also rock, but collecting the entire series isn't easy.
Image and Top Cow are my favorite publishers, and since Top Cow is partnered with Image I usually just save time by only mentioning Image. Image has plenty of miniseries that rock, but no publisher has as many bad-ass miniseries as Avatar Press.
A suggestion to anyone who reads and enjoys Liefeld's work - don't tell anyone about it. Seriously, comics fans will shun you for that.
haha, making this less of an ad for image comics and answering the question... i suggest the death (and rebirth) of superman, the our worlds at war storyline, and most recently blackest night and brightest day.
What do you like at Marvel, specifically. If you like the everyman sort of angle (like Spiderman), you might like Booster Gold and The Flash (slightly surreal). If you like bombastic Action the last volume of JLA (ran through most of the last decade) is the best also the current Green Lantern is great.
If neither of these are your thing, tell us what you've been reading and I'm sure I'll have some suggestions.