7TV from Crooked Dice.
It allows you to go in any direction you wish from humans to aliens (and with the optional 7ombie, 7th Voyage (think Sinbad) and Doctor Who books the game can move into these areas too) and only requires a small group of miniatures for a functional game. This means that I now tend to focus on my painting as opposed to building huge armies.
Appropriate miniatures may come from literaly any manufacturer, I have Crooked Dice, Heresy, Black Tree, Artizan, Hasslefree, Gripping Beast, West Wind and many more.
The rules have a good following and may be used for a multitude of settings, are elegant and well supported by their own forum and facebook page and do seem to attract some top notch painters.
I am currently painting Hasslefree Modern Troopers for use in a multitude of settings all based on the 7TV rules including SG1 and BSG (fan made rules available on the forum).
Having discovered this I sold off around a thousand imperial guard and a 25 year collection of GW stuff.
I have zombies, Daleks, Ninjas and Crab People amongst many others and do not find myself getting bogged down or bored the way I used to.
The only other rules I use are Dead mans Hand with small western gangs and sarissa/battleflag buildings.
(I have also found the Sarissa city buildings great for 7TV)
It has changed the way I paint and game and just maybe saved the hobby for me as I was beginning to get bored and Jaded.
Have not encountered any power gaming yet and nobody has even mentioned tournament play.
I love 'em. Check out their Facebook and Crooked Dice forum. (their miniature range has some gems too, from Dr Who, Captain Scarlet, Blakes 7, Bond and many more)
I do not work for them btw.