Serious Eats - seriouseats.com

Beaver's Deli mustard! Unbelievable stuff. The huge seeds give it a lot of texture, and it's just perfectly balanced. I went through a whole bottle, and maybe made 3 or 4 sandwiches with it - I'd just squeeze out a little bit on my finger and eat it raw.

Silver Springs: Beer N' Brat mustard....my favorite!

Plochman's natural stone ground.

Maille Dijon is super, too - good for adding a bitey kick to soups, and for rubbing on roast chicken [pre-roast].

I practically grew up on French's Honey mustard, and later became partial to Deli Mustards - Grey Poupon's always been good to me
Inglehoffer's another brand that I've tried and liked

Have never seen Beaver mustard, anyone in the northeast know where it's available?

Maille old style! Good on sandwiches, or with honey and baked on chicken. Also so good to eat straight out of the jar. Mm.

I'll give another nod to Maille Dijon. My standard "nuthin fancy" mustard is Gulden's. Inglehoffer's Extra Hot is for when I'm in the mood for horseradish (and that means I want extreme nasal burning).

Pardon me, would you have any Grey Poupon?

Nance's Sharp and Creamy mustard. Like a creamy Dijon. I like it with a slice of ham, apple, and cheddar on toast. Yum!

Fox Hollow Farms mustard! da beeeeeeeeeeeest

Try Stadium Mustard - it's the best!!!

www.stadiummustard.com (altho it looks like you can only order by the case...)

Inglehoffe's Sweet Hot... soooo good.

DH's choice would be Koop's Arizona Heat.

Seriously, though, doesn't it make sense to break the mustards down into traditional (yellow/brown), dijon and variants, and fancy?

@sunbyrne - Yes on the Nance's!

Maille cassis mustard! Delicious. (Particularly on French fries; forgive me.)

Honeycup mustard. Vermont Maple Horseradish Mustard, which appears not to be available separately on their web site. French's classic yellow on hot dogs, since the hot dog wouldn't taste like a hot dog to me otherwise.

Raye's Sweet & Spicy mustard is my new go to sandwich slatherer, I found it at World Market here in Florida and will stock up incase they pull it. My back up mustard is Ben's Sweet Hot. Both are outstanding full-flavored condiments I use for sandwiches and as additions to my feeble attempts at making sauces.

Pommery Green Peppercorn Mustard, or, being all chichi - Moutarde au Poivre Vert. This stuff is so good I'll just eat a spoonful of it they way one does with peanut butter. It's not cheap, but man, I go through it like like wildfire.

Ditto Coleman's, but for everyday I like the Natural Value yellow mustard that's cheap at my co-op

Yellow mustard doesn't taste like mustard to me. It tastes like Vinegar.
Maille's my brand for sure.
@Expatslat - oh man it's a deadly blend!! soo good
I'm a fan of most President's Choice condiments as well.

Kosciusko Spicy Brown Mustard

Maille Dijon, like many others have said. Though I also have developed a fondness for Grey Poupon coarse ground mustard, which I often use in my cooking as well.

Bertman's Ballpark Mustard - absolutely the best! (I live in CT but order it from OH)

Stonewall Kitchen's Blue Cheese & Herb Mustard, amazing flavors abound.

Maille regular and whole grain Dijon
Gulden's Spicy Brown Mustard
French's Yellow

Raye’s “Down East Schooner” Mustard. It was also the gold medal winner in the 'Classic American Yellow Mustard' category at the 2009 Mustard Competition.

My work's home base is in Switzerland. There, I discovered Thomy’s Senf. I thought at first, it was toothpaste, as it's sold in a tube (very portable). Thomy is a Swiss brand that produces food products such as mayonnaise, mustard, salad dressings, and the best [again in a tube] tomato paste. If you can get a tube of this Swiss equivalent to the U.S. 'every home has some' of French's Yellow, you'll love it. It's creamy and thick, has a nice sharpness and is packed with amazing flavor.

I like a lot of different kinds, all mentioned above, but wanted to put in a vote of confidence for the Garlic Dijon Aioli at Trader Joe's. It's goood.

-Ben