Recently a hack of MUGEN called MUGEN Plus came out. It allows for hires characters and stages as well as the old lowres ones. You can get it at Random Select under Download Mugen. People who already have WinMugen can simply replace their winmugen.exe with the one from the Plus download. Unfortunately your fonts and character select screen will now appear small. You can go through and resize your screenpack, but it's pretty tedious. I've attached my resized screenpack shown in the above screens.
I've been refining my character roaster the past couple of days. Updating and replacing characters where need be. I've found many links to the original authors sites. I'll try posting as many of those here as I can find again. Most new stuff can be found by looking at the Mugen Guild releases forum.
HiRes Stuff:
Stages:
So far I've only found a few of these. But the ones I've found are superb. First off, Kung Fu Man's posted some here. I was only really interested in the Night of Walpurgis stage to replace the lowres one I had. Ziltama makes amazing stages with all kinds of stuff going on in the background. The Sky Battle stage in my first screenshot is his. He has great SMB3 stages and a nice looking hires screenpack too.
Characters:
Guilty Gear: Akutagawa made an Order version of Sol Badguy and a Ky. I had a harder time finding a hires version of regular Sol, but finally found the download links for Amachi's on his news page. Muteki makes practically all the other characters. Note that I had to use winrar to unzip his characters that are in parts because winzip wouldn't for some reason.
Goku: toskomics' hires Goku is what I used to replace the old Goku someone recommended at one point. The password for the download is toskomics if you didn't figure it out. You have to see this one's Spirit Bomb attack. It's of the few DBZ characters worth keeping.
Lowres Characters:
I'll start with the three legendary characters created by Reu (who recently passed on :(). His crazy comboable Evil Ken, Evil Ryu, and Dragon Claw can all be found at the Mugen Institute.
My favorite characters that can be found at Random Select's Hosted Creations-Characters section are Big Eli King's Tetsu, Dark Chun-Li. Tetsu is at heart a Ryu clone from some fairly unknown game. He's my new favorite with high comboability (air combos :D) and nice supers. Dark Chun-Li is more interesting then I thought she would be. She floats everywhere and has a possessed purple afterimage and creepy laugh. His Venom is probably the best out there and his Aska is good too. ShinRyoga's drawn Super Mario and Super Luigi are there. Splode's Randy from Guardian Heroes is somewhere there too.
Phantom of the Server has created many great Capcom characters. All of them have their own style that's quite different from the more faithful MUGEN conversions. Personally I find these far more fun to play as. His Ryu is special in that he has Evil and Master modes if you select certain palletes. I've kept ALL of his characters in my MUGEN.
Riot of the Blood Rehabilitation Center is another great source of characters. Orochi Herman's Setsuna, Kagami, Raiya, and Shadow Dio are my favorites. I also enjoy Mattasaur's Kabuki Klash characters.
Speaking of Kabuki Klash characters, I've had Tsunade, a little girl with an axe, for quite a long time. I've always found her axe spin to be fairly cheap, but she's cute and you can usually avoid it. The creator's site is Sunny World and there seem to be some other characters that look worth having there too.
I have the Manjimaru from Mugen China. They have a crapload of other characters.
Zelgadis made the best Awakened Kaede (originally from the Last Blade series, but this is a KOF version). Here's a direct link to the character download because adblock doesn't seem to like that site.
Rainman's Tales of characters are the best around. He has a Cless, Rimle, and Kyle.
Warusaki3 makes very accurate CVS conversions. I only have his Hibiki and Athena at the moment. His non-CVS works can be found here. I like the bikini clad Goddess Athena myself.
Byakko's CVS characters. I like all of them, Another Kyo was the first I got and liked.
Andre has a lovely Mai. Yeah, there is a “Sexy” version for people who want that kind of thing.
Ribeiro is the one that made the hand drawn(I think?) Megaman.EXE. His Hiei is also good.
Trinity Mugen is another site with a lot of good characters. I like Jesuszilla's CVSZero here.
Hsieh made what I would guess is the most popular Jin Satome. His Roll is the best and his Morrigan is probably the old one that has the really hard AI (POTS Morrigan is better IMO).
Inverse's Slash, Daolong, and Sho are classic.
Melty Blood Characters. All of them are pretty much perfect. The Shiki is huge because it has an assload of voice files in it.
I like Master Gouken's Haohmaru over Warusaki's for some reason.
I wanted a Terry at one point and Ultimate Terry by K.O.D. seemed to fit the bill nicely.
One of the newer Spiderman's to come out is SethZankuten's. It has a few special pallete modes and nasty AI.
Aiduzzi makes some creepy original characters. Ella is my favorite, has has a chainsaw and a stuffed bear that comes out of places o_o.
That's about it. There are a few characters I couldn't refind. Oh well.