How can I become immune to fall damage?
I don’t mean things like feather fall that slow your descent or flight that prevents it from happening altogether; I'm more looking for an option that lets you fall, brush yourself off, and leave like nothing happened.
Non-spell solutions are preferred. I’m character building in E6 for a contest; Pathfinder content isn't allowed. The distance of the fall does not matter; I need something more universal.
Note: this answer has been posted before I knew it was for e6.
Fall damage is, well... damage.
So, the trivial answer is: be immune to damage.
Find a way to gain regeneration (unless it's damage of a specific type, it gets converted to nonlethal damage) on a character that is immune to nonlethal damage.
Being actually immune to the nonlethal damage is for the "it did nothing to me" effect, but if crashing really hard and then springing back with regeneration is ok, just regeneration will do.
For immunity to nonlethal damage, take enough levels in the Warforged Juggernaut or Bone Knight (Five Nations) prestige classes, both from the Eberron setting, or you can use a number of spells that provide it, as long as they don't turn you into a construct or an undead, which would bring your Con to - and remove your regeneration.
The boots of landing (Magic Item Compendium 77–8) (500 gp; 1 lb.), in part, says, "While wearing boots of landing, you land on your feet no matter how far you fall, and you take 2 fewer dice of damage from the fall than normal (thus, a fall of 20 feet or less deals you no damage)." To be clear, the MIC update of the boots removes the 1/day limit of the linked version from the Expanded Psionics Handbook. (And if the MIC can even make this change should be answered by the table's primary sources; see here.)
Adding nine boots of landing effects to existing boots of landing has a price of 7,500 gp according to the MIC on Improving Magic Items (233), therefore 8,000 gp total. If the DM rules that the effects of multiple boots of landing don't combine for a cumulative effect, you might be out of luck acquiring immunity to falling damage with a reasonable expenditure of resources. However, if the DM rules that the effects of multiple boots of landing are cumulative then the wearer of the boots of landing-landing-landing-landing-landing-landing-landing-landing-landing-landing should be dealt no damage by most falls as the damage is reduced by 20 dice (see here).
Similar but less useful is the magic armor special ability landing (12) (4,000 gp; 0 lbs.) that had its SRD prerequisite for creation changed to the feather fall spell but was otherwise unchanged: The wearer "ignore[s] any damage dealt by the first 60 feet of a fall." However, since the first 60 ft. of a fall only happens once, adding the ability landing to one's armor more than once is a waste. Still, if the creature's not going higher than 60 ft. there's no question that the ability landing works. (And it's 80 ft. if the creature's also wearing normal boots of landing, so there's that.)
(This DM would likely allow the 10-boots workaround simply because what's desired seems unreasonably difficult to acquire otherwise and theoretically inoffensive but would make it clear that this sets no precedent.)
Otherwise, incorporeality (Dungeon Master's Guide 294–5), the 1st-level Sor/Wiz spell feather fall [trans] (Player's Handbook 229), the special ability slow fall (like that of the monk), and abilities, items, and spells that have like effects seem to be what the game expects folks to use to avoid falling damage, and none of those are particularly useful for the question's purposes. I mean, for example, like this fine answer mentions, a blanket immunity to damage works, but that is often considered unbalanced.
