It is not never ending - but Vexed, or Vexed DLX has about 1600 puzzles, so for for most purposes it is never ending... On a similar note TanZen or TanZen HD has around 500 puzzles - again will take a very long time to complete... These are 2 in the puzzle category BTW although you probably know that... Word Quest Plus Link (I put that in there as there is a copy cat with a very poor imitation to this game) is a word search program, very well done, universal, and has 4 different play modes and obviously generates random boards each time.. There is a lite as well to check it out. Crosswords by Standalone is also never ending as it grabs new puzzles every day. Not sure if any of this is what you are looking for, but good luck on your quest, and please let us know what you wound up with, I would be curious to know.
There is Sigma, and the newly released Helsing's Fire, both highly recommended by me. There is too Pix'n Love Rush and a bunch others I can't remember...
One other game is Unblock me (It's full of content) - I'm looking for a game like that. Crosswords has been on my To Get list for a while. Although the Price is outrageous. I looked at the developers website for Vexed DLX, and the fact that they have "FarmVille Exposed" and such things made me frown. Unless they remove that, I will not be purchasing anything from them. I've looked at Word Quest Pro - and I don't like the screenshots. They are very cluttered and I'm only looking for a game that is clean and to the point. As for word games (I love those things) I am always looking for one and especially know that I made this thread. So please keep your suggestions coming and I'm terrible sorry for continuously changing my mind.
Super Quick Hook is a never ending side-scrolling adventure, no puzzle elements though. Miner Disturbance has a randomly generated Volcano, so not quite never ending, but it is a puzzle, side-scrolling, adventure game, and the volcano is randomly generated. Action-Buggy by donut games is a side scrolling endless action game. Pix n' Love Rush is a side-scrolling, never ending, adventure game, and the scoring is a little puzzling I guess so it may be your best bet. Above is an endless side scrolling game, it's a plat former mix between canabalt and doodle jump, but the art direction and polish is much higher than either of those games, and I find the gameplay much more engrossing and rewarding. So I guess not all of those fit all your criteria but they may be nice. It's hard to find an endless mode in a side-scrolling puzzle game though. Try out ABCA, Wordcrasher, or RSS Hangman. All are top notch.
Well the quest for knights onrush is getting a full game, which I hope will have an actual endless mode, right now the quest for knights onrush only lets you get to 7020, then it automatically ends the game, so I can't wait for the full game.
side scrolling never ending game: ACTION BUGGY, ACTION HERO (or something like that), both by donut games. you could also get cube runner, CYBERRUNNER.
Wheeler's Treasure !! I forgot, but it is a never ending randomly generated side scrolling platformer(of sorts), it also has some racing elements, a good sense of progression between games(upgrades), and a good challange+fun factor. You probably already have it, but wanted to give it a mention.
Here are the one's I know of: Solomon's Keep Sword of Fargoal 100 Rogues Cube Runner Cyber Runner Doodle Jump Run! Pixn' Love Rush EDIT: I forgot the obvious and probably one of the best ones: Space Invaders Infinity Gene.
Maybe that works for the OP, but a game with an editor, even if really great, doesn't scratch that itch for me. I want levels whipped out on a whim, not needing to make them on my own or constantly find friend's levels to keep stuff going.
Go!Go!Soccer A really fun game that I guess could be considered as endless is Sorter. I highly recommend it, and it was the best game of May for us.