Now that TR brings up ROM hacks, I will bring up one of my recent favorite hacks.
Sonic the Hedgehog Classic HeroesTake Sonic 2. Add Knuckles as a playable character, every level (Including the Special Stages) from Sonic 1, save game support, the special shields from Sonic 3, and 3 player mode. Make fixes so it's in a nice playable package. Done.

Aside from that, I've added some games to my current playlist (No pun intended, as that's usually a term for multimedia playing stuff).
-Vampire - Darkstalkers Collection (PS2)
-Vampire - Darkstalkers Chronicle (DC)
-Wrestle Kingdom 2 (PS2)
I've just been simming matches like crazy with Wrestle Kingdom 2, and will probably tackle the card-based Campaign Mode sooner than later. As for the Darkstalkers games, I just started playing the series because of several characters from the series being included in Capcom Fighting Evolution (Which the way they meshed the fighting styles from the represented games was done quite well, in my book). Collection has all five of the original games (With Arrange Mode for Vampire Savior as well as the Japan only "V2" Night Warriors and Vampire Savior), while Chronicle is basically the series' equalivent of Hyper Street Fighter 2 (And then some - the characters that weren't in the original Darkstalkers and Night Warriors have movesets that match the gameplay styles of those), with all three rulesets from the various games available. If you are unable to play Chronicle on the Dreamcast, it was released internationally with additional features on the PSP as Darkstalkers Chronicle - The Chaos Tower.
As for who I'm playing as, I'm still getting to grips with all the more advanced gameplay mechanics, so I've been using Victor, Huitzil (AKA Phobos), Sasquatch, and Oboro Bishamon, who use fighting styles that I feel most comfortable with in most fighting games. Victor and Sasquatch because I play as Zangief a lot in the Street Fighter games (And because Sasquatch has some similarities of Sub-Zero, who I main in the Mortal Kombat games), Huitzil because of his hovering ability and variety of projectiles, and Oboro Bishamon because he's the game's equalivent of Shin Akuma (Gouki) and therefore has so much combo capacity. (No, I won't use Oboro against a human player - that would be just plain mean.) Right now I would say Sasquatch is my main.
Most likely I'll be tackling Demitri and Morrigan next, though it will take a brief amount of time for me to get used to the fact that Demitri doesn't have an exact recreation of Ryu's Hurricane Kick.
As for what the future holds, I may get into Visual PinMAME again soon after reading that the good doctor is playing The Pinball Arcade on his Vita. I always liked pinball myself, shame there aren't a lot of places where I live that have actual tables anymore. (Protip - If you're a retro gamer and like both pinball and Pac-Man, try Baby Pac-Man out at some point. It's essentially both genres combined - you'll have to play it yourself to see what I mean.)
Then of course there's Digimon Adventure coming out for the PSP in about a week's time, but you all knew I was going to play that one anyway.
Mini-wall of text hits you for 2,013 damage. Your move.