Comics!? Did someone say comics!? Oh hell yes I love me some comics... ok favorite Trades? Ok. Preacher was excellent, you like Garth Ennis? Hmm, well I am huge on super heroes mostly but let me give you a list of some of my favorites:

Ok Hellblazer is definently up there, specifically the Garth Ennis, Brian Azurello, Warren Ellis, and Alan Moore runs. You can find a list here: http://www.hellblazertrades.com/

Ok I'll keep going I have nothing else to do:

Exterminators Volume 1,2, and 3 by Simon Oliver
The Walking Dead by Robert Kirkman
Invincible (Read the first 3 trades, if you're not hooked somethings wrong with you!)
Transmetropolitan

If you've never read the Watchmen, I would get that next, that book is so important to comic book readers its not funny. Alan Moore's finest work.

I'd also reccommend picking up the Ed Brubaker Captain America run, it's fantastic.

Brian K. Vaughn's first 3 volumes of Run Aways is spectacular.

The Mark Millar Spider-Man Marvel Knights has 4 volumes that are really quite good.

Try the Astonishing X-Men by Joss Whedon, that is a a great book too.

Also try Ultimates 1 and Ultimates 2 (each has 2 trades) the art is spectacular and the modern day avengers story is great.

Also I am a huge Warren Ellis fan, so here is some great stuff:
Next Wave: Agents of H.A.T.E. Volume 1 & 2
Desolation Jones
Planetary (He didn't do all of em, so start at the beginning)

Also I would highly reccommend you read The Authority, check amazon start at the beginning, and I dare you not to love it. I would recommend this next since you just finished Preacher and this book is so epic in nature. Just wait till you get to the trade where they fight God.

Hope this helps!

Anything by Chuck Palahniuk. Um... and comics. Lots of comics. Anything by Joss Whedon (Astonishing X-Men, Upcoming Runaways) Ed Brubaker (Captain America) and Brian Bendis (New Avengers, Ultimate Spiderman) are great.

Joss Whedon is my master now.

One of the best Office episodes. Joss Whedon is my master now.

pretty much an instant upvote for Joss Whedon. great movie too.

Joss Whedon is God.

http://en.wikipedia.org/wiki/R._tam_sessions
The R. Tam sessions are a series of five short videos released by Joss Whedon over the internet, which were set within his fictional "Firefly" universe. They chronicled several of the early in-universe interviews with the emotionally troubled Firefly character River Tam.
Although released unofficially, the videos were meant as a form of viral marketing for the 2005 film "Serenity"...
Set before the events of the "Firefly" television series and the film "Serenity", the R. Tam sessions depict excerpts of counseling sessions with the character River Tam while she is held at a "learning facility" known only as "The Academy." The counselor in these sessions is played by Joss Whedon himself. The videos shed some light on the experiments and torture "The Academy" conducted on River. They "document" her change from a shy child prodigy to the mentally unstable character of the television series.

*gasp*
What've you been waiting for?
Seriously, though - "Firefly" was a real precursor to "BSG", in terms of "reality" sci-fi, with real guns and the in-camera illusion special effects. Not as angsty as "BSG", though - still dramatic, but with Joss Whedon's lighter touch.