The Great Library is a must have on any map type. 7bpt (6*1.25 = 7.5, rounded down is 7) is nothing to laugh at at that point, but it's really the free GSP (8, 2 from the wonder, plus six from the specialists) that makes this wonder a necessity.
The Great Lighthouse is a necessity on any water based map. The extra trade route are negligable until your cities are well developed, but the longevity of this wonder makes it very much worthwhile to build.
That's really about it in terms of must have wonders. The Pentagon, the Three Gorges Dam, and the Eiffel Tower are all very nice as well, though certainly not must have. The modern happiness resources are good to control, but again, they are not must have wonders.
The Oracle is really overrated. It's classically used for either a 350 beaker or a 450 (400?) beaker tech, and only seems potent because those techs seem otherwise prohibitive to research on your own, but they're not.