One called ONS-2Fort is probably the most unusual map I've played. It's pretty small - actually it's more like a deathmatch level with a handful of powernodes. Only problem is that it gets really old because it's balanced to the point that without a quick countdown to overtime, a single match can last like an hour.
ONS-Cell is a pretty funky one too. It's a large dark stadium with most of the powernodes in short tunnels off of the main area. A cool map.
ONS-TopGun consists of three islands - one for each core, and one with a lone powernode on it. And a ton of Raptors. A neat map, but very unusual. Still fun though.
ONS-TankWars is another single powernode map. Each team gets something like ten tanks, and there's pretty much no strategy involved. Fun as hell.
ONS-Torlanights is a favorite of mine, right next to ArcticStronghold and Severance. It's Torlan, but very dark (except for in the bases). You can sneak up on people if you're quiet. Or see turn around to see a blinding light and you get to know how a deer feels during its final moments. The cricket ambience is nice too.