Birmingham's victory at Reading, coupled with some poor Blades finishing in south London means Alex McLeish's side have earned an instant top-flight return, while United join the Royals, Burnley and Preston in the play-off lottery.
Greg Halford and Kyle Naughton both missed early half-chances for Kevin Blackwell's side, while Neil Danns went close in a low-key opening 20 minutes.
Darius Henderson headed narrowly wide in United's first real opening before Palace keeper Julian Speroni made the first of a string of impressive saves in the 32nd minute, somehow tipping over Chris Morgan's downward header.
Victor Moses missed a glorious chance to put Palace ahead moments after the break - but Paddy Kenny won the battle of wits against the Eagles teenager.
Danns then missed two gilt-edged chances to shatter United's automatic promotion dreams.
First, in the 57th minute, the midfielder somehow blasted wide from ten yards with only Kenny to beat, then two minutes later the midfielder hammered a half-volley straight at the Blades keeper, after the ball broke to him invitingly just inside the box.
Speroni bettered his opposite number's heroics twice in the space of 30 seconds in the 62nd minute.
The Argentine somehow kept out Jamie Ward's point-blank effort after a Stephen Quinn pass before tipping over Halford's towering back-post header seconds later to frustrate the Yorkshire side.
Throwing bodies forward at every possible opportunity, United nearly got caught in the 79th minute, but substitute Lee Hills failed to capitalise on some clever work from Shefki Kuqi and Rui Fonte.
United came agonisingly close to stealing all three points in injury time, but Morgan's header grazed the post, before Arturo Lupoli made a hash of Danny Webber's low cross in the dying seconds as it ended goalless.