cols(x) mixin adapted off of Upstatement's ui-block mixin.

cols.scss

@mixin cols($col-num: 2, $width-1: 0, $width-2: 0, $width-3: 0, $width-4: 0, $width-last: 0, $margin-r:5% ) {
	
	@include pie-clearfix;
	$var-list: $col-num, $width-1, $width-2, $width-3, $width-4, $width-last, $margin-r;

	//Discovers margin option
	@for $num from 1 through length($var-list) {
		$value: nth($var-list, $num);
		@if $num == ($col-num + 2){
			@if $num < length($var-list) {
				@if type_of($value) == number {
					@if unit($value) == "%" {
						$margin-r: $value;
					}
				}
			}
		}
	}

	//Flip functionality
	$flip: false;
	@each $var in $var-list {
		@if $var == flip {
			$flip: true;
		}
	}
	@if $col-num == flip { $col-num: 2; }
	@if $margin-r == flip { $margin-r: 5%; }
	@if $width-1 == flip { $width-1: 0; }
	@if $width-2 == flip { $width-2: 0; }
	@if $width-3 == flip { $width-3: 0; }
	@if $width-4 == flip { $width-4: 0; }
	//eo flip functionality

	//Default values given no supplied values
	@if $width-1 == 0 { $width-1: 100% / $col-num; }
	@if $width-2 == 0 { $width-2: 100% / $col-num; }
	@if $width-3 == 0 { $width-3: 100% / $col-num; }
	@if $width-4 == 0 { $width-4: 100% / $col-num; }
	@if $width-last == 0 { $width-last: 100% / $col-num; }

	//width-last needs to be determined no matter what, in case it's not supplied
	@if $col-num == 5 { $width-last: 100% - $width-4 - $width-3 - $width-2 - $width-1; }
	@if $col-num == 4 { $width-last: 100% - $width-3 - $width-2 - $width-1; }
	@if $col-num == 3 { $width-last: 100% - $width-2 - $width-1; }
	@if $col-num == 2 { $width-last: 100% - $width-1; }

	//Needed to reset var-list for some reason
	$var-list: $col-num, $width-1, $width-2, $width-3, $width-4, $width-last, $margin-r;
	$name-list: first, second, third, fourth, fifth;

	//First col - second-to-last col
	@for $num from 2 through $col-num {
		$width: nth($var-list, $num);
		$name: nth($name-list, ($num - 1));
		$col: $num - 1;
		> .col-#{$col},
		> .col.#{$name} {
			margin-right: $margin-r/($col-num - 1);
			width: $width - ($margin-r/$col-num);
			@include float-left;
			@if $flip == true {
				@include float-right;
			}
		}
	}	

	//Last col
	> .col-#{$col-num},
	> .col.#{nth($name-list, $col-num)},
	> .col.last {
		width: $width-last - ($margin-r/$col-num);
		@include float-left;
		margin-right: 0;		
	}
}

examples.scss

.examples { 
 
 @include cols;
 @include cols(2);
 @include cols(flip);
 
 @include cols(2, 60%, 40%);
 @include cols(2, 60%, 40%, flip);
 @include cols(2, 60%, 40%, 2.5%);
 @include cols(2, 60%, 40%, 2.5%, flip);
 
 @include cols(3);
 @include cols(3, 20%, 60%, 20%);
 @include cols(3, 20%, 60%, 20%, 2.5%);
 
 @include cols(4);
 @include cols(4, 10%, 40%, 25%, 25%);
 @include cols(4, 10%, 40%, 25%, 25%, 2.5%);
 
 @include cols(5);
 @include cols(5, 20%, 40%, 10%, 10%, 20%);
 @include cols(5, 20%, 40%, 10%, 10%, 20%, 2.5%);
 
}