There are several general ways:
1. Take multiple two-handed weapons with reach. I.e. play a diopsid (Dragon Compendium LA +1 race with 4 hands)
2. Take multiple weapons with reach, but use them as one-handed weapons. I.e. play an orc with two Spiked Chains, that are designed for small creatures.
3. Take multiple weapons with reach by using one in two hands and one without hands. I.e. play a monk with a spiked chain (Unarmed Strike/Spiked Chain) or use armor spikes as secondary weapon or hidden weapons...
4. Increase the reach of regular weapons. Examples:
Getting Reach
Warshaper 3, ecl 8, PrC (CW), +5': so easy and beneficial. Be a changeling or take a level in Bear Warrior for easy entry.
Atavist 5 (aggressive spirit), ecl 10, PrC (RoE), +5': I think this is not a thing to pick up, but might be green for monks or Mind Blade users.
Umbral Disciple 10, ecl 15, (MoI), PrC +5' per essentia: Nothing easy to pick up, but gets blue in some self-flanking rogue-builds that deal incredible dps at ranged melee.
Shadowblade 9, ecl 14, PrC (ToM), +10', limited use: That class would be good for a rogue if it would have more skill points.
Deformity (tall), Vile Feat (HoH), +5': Two feats for +5ft reach ok.
Inhuman Reach, Aberrant Feat (LoM), +5': Depending on your DM you might get it by being a changeling or Elan
Long Reach, Feat (UE), +5' with short or longspears, on your turn only: It's a fighter feat that has it's uses for keeping foes at bay.
Long Arm, Graft (FF), +5': Really cheap, but gets you easily evil, although the wis dmg can be overcome pretty easy.
Mark of Malbolge, Feat (FC2) +5' for 1 round, see text: I'm not really familiar with this, but since it uses actions it won't be too great.
Bestial Charge, Feat (CC), +5', see text: This is a pretty strong feat for a charging druid.
Lunging Strike, Feat (PHB2), +5', see text: full round action for a single attack is really bad.
Dancing Blade Form, Stance, (ToB) +5' only on your turn: It's only during your turn and a level 5 stance. Not too great.
Reach, Power, +5': If you want it better, be psionic... Really cheap for 3points 1r/lvl.