The Sip ‘n Dip Lounge, Great Falls, MT
I can't attest to the quality of the drinks, but for atmosphere and appearance, it appears that the Sip 'n Dip Lounge in Great Falls, Montana, outshines even Ft. Lauderdale's Wreck Bar by combining an underground window with a view of live mermaids cavorting in the hotel swimming pool with a full-on tiki bar interior.
The bar features entertainment from Piano Pat who has played at the location five nights a week since its opening in 1962.
I can't see making a pilgrimage to Montana for this one bar, but GQ Magazine saw fit in 2003 to name it "#1 bar on Earth worth flying for," as it's attached to the O'Hare Motor Inn.
Visit the Sip 'n Dip Lounge official site