I do a graphic novel book group at a local bookstore, and last meeting someone mentioned Deadpool. I know the character, but never read his series. So I figure who better to ask than you guys. What would be a good trade paperback volume to do?

It should be:

A good, fun story.

Something reasonably mainstream. Something typical Deadpool

Something that's a good stand-alone, that doesn't require a lot of knowledge of the character's history or the Marvel Universe in general.

Deadpool: Merc with a Mouth.

It involves Deadpool attempting to return a bodiless zombie version of himself back to the Zombieverse. It's good on its own.

The Deadpool Team-Up titles are, for the most part, very enjoyable. Different artists and writers on each issue make every one a standalone story, so pick and choose what interests you.
Standouts are:
Deadpool & Gorilla-Man
Deadpool & Iron Fist
Deadpool & Hercules
Deadpool & Thor
Deadpool & The Watcher

Personally, I think the best Deadpool story to start with is Deadpool: Suicide Kings. There may be one character you aren't familiar with, but he doesn't really need explanation as he is mostly a plot device to keep things going.

Great story, good action, great team ups, super good dialogue, and classic Deadpoolisms. What's more to ask for?

After that I would HIGHLY recommend reading Dainel Way's entire run of Deapool, as it is quite funny and gives you incite into the little things about Deadpool. Yes it is long, but it is greatly worth it especially the Secret Invasion, Dark Reign, and Dead arcs.

Hope you enjoy!

i dont recommend any deadpool lol

Wade Wilson's war was a good mini. I'm tempted to say the Deadpool Corps, but the only good thing that came out of that was my custom clix figure.

The Cable and Deadpool series was pretty enjoyable

He's going to be in the new Thunderbolts!

Also, I loved the arc where he was a pirate and the one he fought the draculas

I just looked that up out of curiosity.
Red Hulk
Deadpool
Punisher
Elektra
Venom (still Thompson)

Yeah, I'll pass on that.
The whole point of that series was, to me, showcasing the more B- and C-list characters that could never hold a title on their own, but were interesting characters nonetheless. That's why I liked Parker's run, although I stopped during Fear Itself because I wanted to read Thunderbolts stories, not another Fear Itself storyline.
Plus Daniel Way writing doesn't do much for me; I actually stopped getting his Deadpool title during the crazy psychiatrist/Evil Frankenpool arc because it was just too ridiculous. Even for Deadpool.
DP's first solo series by Joe Kelly is still some of the most entertaining LOL-worthy stuff I've read. Classic, classic stuff. The Christopher Priest run immediately after that has some of the best stuff ever, especially his interactions with his "roommates" at the time - Constrictor and Titania.
I actually really liked the Udon Agent X stories, too.

Way is hit and miss as of late they are bad but earlier are good. Suicide Kings is good. his classic tpb sets are good as well

Cable and Deadpool was my favorite. As mentioned above Deadpool: Merc With A Mouth was pretty consistently good. Daniel Way's current run of Deadpool has sucked lately imo. But the early issues like probably #1-18ish were all hilarious. Currently all DP books suck. Wish they would pass DP main series on to someone else and give a different take on him.

good news! (look up marvel now)

also, I did like the Dead story line from him

Feel the same way about Way (heh). DP was on a roll early on, Way's writing got a little tried after that.

My suggestion would be the Uncanny X-Force series. Deadpool is in it and has a lot of wacky moments.

The only Deadpool I can endorse: