lol that surprisingly the Best Buy "expert" is correct. for 100% compatibility (because they pretest the sticks in dual channel motherboards before packaging them), go with Dual Channel spec'd RAM. 2 of the same brand/model sticks are not GUARANTEED to work though they MAY.
edit: here's an example: http://www.ocztechnology.com/products/memory/ocz_ddr_pc_3200_value_series_dual_channel
these particular sticks aren't the fastest in the world by any means, but they are 100% guaranteed to work in dual channel mode. also, OCZ has BY FAR the best customer service/support in the PC industry.