There's this mod which adds one new unit to each race in StarCraft. They take a long time to build and cost a lot of money, so they don't ruin the game, despite their strength. They're also not unique units - you can have more than one of them. Playing the mod is simple. Just download it and play multiplayer on the mods own PvPGN server. I'm not entirely sure how to get lan latency working with this mod, though.
The reason that I am interested in this mod, is that it actually seems rather balanced. The units seem like they don't take over the game too much or ruin it - StarCraft's gameplay is still intact. It's just like another expansion pack.
So I am creating a Skype group for people who want to play this mod. Reply to this thread or PM me, and I will PM you the Skype information.