Lunging Strike is a feat from PHB2, requires a +6 BAB, and lets you make one attack with 5 feet of extra reach each round. A bit more to it than that, but I won't elaborate since it's not OGC.
Pathfinder has a similar Lunge feat in its core rules, IIRC, and as others mentioned, the Tome of Battle has a Stance that gives you +5 feet of reach on your turn (but not on other turns, so it doesn't help with attacks of opportunity). Dancing Blade Form, requires 2 other Iron Heart maneuvers and/or stances, so if you wanted to take it without Warblade levels, you'd need to first take 1 or 2 copies of the Martial Study feat for Iron Heart maneuvers, then a copy of the Martial Stance feat for Dancing Blade Form. And since your initiator level is only half your actual character level when you're not a martial adept, you'd have to wait quite a while to qualify for those particular copies of the feats (18th-level for Martial Stance - Dancing Blade Form). A few levels of Warblade would hasten and cheapen access to them, of course.