Actually, I think I have a theory as to why I'm suddenly seeing more brands at grocery stores as of late: because they're selling wine now. Typically, it was fairly common to find Bicycle decks in a grocery store usually at the check-out lines, or dangling from a shelf down whatever aisle had chips and/or liter bottles of soft drinks - but now that stores are allowed to sell wine, there's usually an end-cap display case full of USPC brands of cards (and occasionally, so others as well) at the wine aisle, I've come to notice.

Now, to answer your question specifically, here's what I can give you as far as a break-down of the brands:
* Bicycle - They're everywhere. Number one product, so it makes sense. Now, while I usually just see Standard Size/Face in most stores, one regional chain down here called Food City carries additional decks, such as Jumbo Index, Pinochle decks, and Bridge-sized decks. I'll also occasionally see a special deck, such as a pink breast cancer deck. Walmart almost always has the Shark decks
* Bee - Surprisingly, for this to be USPC's other top brand, I only see these at Food City (it's where I got mine), I never see them anywhere else. I also see them in Jumbo Index.
* Hoyle - I used to see these almost exclusively at book stores like Books-A-Million and Barnes & Noble, but another one of our regional chains, Kroger (despite being headquartered in Ohio, is a mostly southern chain) has been carrying the traditional Shellback decks - usually in a two-pack of red and blue (as Bicycle often comes in), but as of late, Kroger has also been carrying plastic Hoyles as well, including the clear ones. Interestingly, one time, I saw a Jumbo Index Hoyle deck at Hobby Lobby, of all places.
* Aviator - Like Hoyle, I used to generally only see these at the book stores, but as of this summer, I began noticing them alongside Bicycle and Bee at most Food City locations; now, they're also popping up at Kroger alongside Bicycle and Hoyle as well.
* Streamline - Food City's the only place I've seen these, and as I mentioned in another thread, they appear to be (at least the deck I purchased anyway) Canadian decks imported from China . . . how they ended up down here in Tennessee is beyond me. They don't see to sell well though, there's usually very few of them in the case, and they're usually always dirt cheap (like a dollar or so) compared to the usually higher Bicycle or Bee decks. Even Aviator decks are selling for like two dollars. So yeah, I can see what you mean about them being a "discount" deck. Of the few decks that I own, it's perhaps my least favorite.
* Maverick - I can confirm they are down here in the south, but I can also tell you that they're not very common either. The only place I've seen them in any kind of regularity is Big Lots, usually in their own miniature cardboard case hanging at the end of a toy aisle). I think I may have also seen them in a Family Dollar at one point, but I can't say for sure, I rarely, if ever, shop at any dollar store other than Dollar General, where they at least have brand-name products. I don't own a Maverick deck, but I have noticed the consensus among most enthusiasts out there is that it was an okay/decent deck until USPC moved to Erlanger, and they've apparently gone straight downhill since. Guess I'm not missing anything.
* Tally Ho - I can also confirm this must be a regional deck, because I've never seen a Tally Ho deck first hand in any store anywhere. I generally hear good things about the deck, though.
* KEM - Never see them.
* As for those novelty decks that you mentioned (Coca-Cola, America, The Dog, etc.) Yup. All at Kroger.
* Congress I've actually never heard of before.  But, based on the information you've given, I guess I could see why (same with KEM).

I should also mention that Food City, in addition to carrying the certain aforementioned deck brands, also carry Bicycle accessories, such as dice, and plastic poker chips.

Interestingly enough, I've noticed that Cartamundi brands are starting to branch out beyond the dollar store chains. Both their Classic and standard Ace brands are being sold alongside the USPC brands at Kroger now, which is really odd - the Classics are sold individually, but the Ace decks are sold in a pack that comes with both red and blue, as well as dice. As I said previously, Classic had pretty much disappeared from dollar stores in favor of standard Ace for a while, but both are being sold again; dollar stores also have Limited Edition Ace decks, but not like the ones we discussed in another thread - dollar store Limited Edition Aces are usually either purple or green. Eagle seems to be exclusive to another regional chain called Ingle's - and likewise, they too are sold ironically alongside Bicycle at check-out. Then again, I haven't shopped at an Ingle's location in a long time (they're not as progressive as other grocery store chains that have long since adopted the whole "super center" layout, but that's not necessarily a bad thing), so I don't know if they've started carrying other brands - if I ever find myself at an Ingle's, I may check for curiosity sake.

So, in short - as far as USPC brands go, Bicycle (and its novelties), Bee, and Streamline remain common; Hoyle and Aviator are becoming more widespread; Maverick is dwindling; the others are virtually nonexistent in these parts. Meanwhile, Cartamundi brands like Classic and Ace are also becoming more widespread.