Exactly what the title says, a specialized rapid reaction armored force. C:BA is the obvious list to use for this purpose, but the following restrictions should be observed for a 'pure' non-BA force:

The following units are not allowed:
• Special Characters
• Honor Guard
• Sanguinary Guard
• Sanguinary Priests
• Death Company
• Death Company Dreadnoughts
• Stormraven Gunship

Additional Rules:
• All units that can take a transport must take one.
• Baal Predators are allowed, but the twin-linked Assault Cannon turret and Heavy Bolter sponsons are required equipment.

The version I'm using for my Space Wolves' Wolf Pack has the following additional prohibited units:
• Scout Squads
• Vanguard Veteran Squads
• Scout Bike Squads
• Devastator Squads

Just a thought for those that like tanks, but don't think their current Marine codex represents a fast-moving armored force very well.