The following GMAT idioms list is based upon official GMAT sentence correction questions that the test-makers publicly released.

Practice these idioms using our proprietary sentence correction questions.

GMAT Idiom Book1 Question2 Answer Page3 Official Guide for GMAT Review (12 ^{th}Edition)x is more than y 12 ^{th}Edition4 686 unlike x, y 12 ^{th}Edition20 694 in contrast with x, y 12 ^{th}Edition20 694 in contrast to x, y 12 ^{th}Edition20 694 estimate to be 12 ^{th}Edition27 698 the same to x as to y 12 ^{th}Edition32 700 depends on whether x 12 ^{th}Edition34 701 so x that y 12 ^{th}Edition37 702 targeted ... at 12 ^{th}Edition40 704 rivalry between x and y 12 ^{th}Edition44 706 expended on 12 ^{th}Edition46 707 the ability ... to 12 ^{th}Edition51 710 x is to y what w is to z 12 ^{th}Edition58 714 amount of x 12 ^{th}Edition74 722 attributes x to y 12 ^{th}Edition79 724 not just because of x, but because of y 12 ^{th}Edition83 726 distinctions between x and y 12 ^{th}Edition96 733 either x or y 12 ^{th}Edition109 740 to consider x y 12 ^{th}Edition117 745 less successful than 12 ^{th}Edition123 748 so x that y 12 ^{th}Edition124 748 x is dated at z years old 12 ^{th}Edition140 756 Official Guide for GMAT Review (11 ^{th}Edition)x is more than y 11 ^{th}Edition2 662 in contrast with x, y 11 ^{th}Edition16 669 estimated to be 11 ^{th}Edition21 671 in danger of 11 ^{th}Edition27 673 seem + infinitive 11 ^{th}Edition29 674 as much as 11 ^{th}Edition30 674 to credit x with 11 ^{th}Edition31 674 as many ... as 11 ^{th}Edition37 676 between x and y 11 ^{th}Edition40 678 require x to do y 11 ^{th}Edition53 684 restrictions on x 11 ^{th}Edition54 685 not only x ... but also y 11 ^{th}Edition55 685 there is no doubt that 11 ^{th}Edition58 686 as a means to 11 ^{th}Edition60 688 attribute x to y 11 ^{th}Edition67 691 as many as 11 ^{th}Edition76 695 used x as y 11 ^{th}Edition79 696 not x, but rather y 11 ^{th}Edition87 700 order x to be y 11 ^{th}Edition92 702 just as x, so y 11 ^{th}Edition99 706 distinguish between x and y 11 ^{th}Edition107 710 both x and y 11 ^{th}Edition112 713 so x that y 11 ^{th}Edition118 716 Official Guide for GMAT Verbal Review not...but Verbal Review 4 256 the rising cost Verbal Review 8 258 range from x to y Verbal Review 9 258 except for + noun Verbal Review 13 260 between x and y Verbal Review 14 260 to mistake x for y Verbal Review 17 261 to think of x as y Verbal Review 20 262 with the aim of + (verb)ing Verbal Review 25 264 not only x ... but also y Verbal Review 46 274 prohibit x from doing y Verbal Review 48 275 more x than y Verbal Review 50 276 not only x ... but also y Verbal Review 52 277 so x that y Verbal Review 58 280 not x, but rather y Verbal Review 60 281 not only ... but also Verbal Review 66 284 in order to x Verbal Review 69 285 as x as Verbal Review 75 288 worried about Verbal Review 81 291 either x or y Verbal Review 84 292 better served by x than by y Verbal Review 89 295 ordered x to do y Verbal Review 90 295 both x and y Verbal Review 93 297 x rose almost as fast as y Verbal Review 94 297 between x and y Verbal Review 95 298 more x than y Verbal Review 98 299 x rather than y Verbal Review 99 300 isolated from Verbal Review 106 300 not only x ... but also y Verbal Review 108 304 as a result of Verbal Review 113 307 This GMAT idioms list is available in PDF format.

For those who are too cheap to buy himself or herself a copy of Manhattan GMAT "Sentence Correction GMAT Preparation Guide", here is the list of the most popular GMAT idioms that are likely already known by native speakers, and must be memorized by non-native speakers (like I am).

http://www.amazon.com/exec/obidos/ASIN/0982423861/iwhite-20

For those who do own a book, take a look at chapter 9, page 142. I am not sure I would be able to memorize all that, but at least I have one more useful guide to refer to.