I only know this place from staying at the Pulitzer, but Zomers, (Prinsengracht 411) serves truly superb seafood and appetizers, coupled with a reasonable wine selection. The atmosphere is a little funky and off-beat, but the staff is friendly and will certainly not make you feel unwelcome if you're by yourself.

Also, further away on Prinsengracht (no. 999 - right off of Vijzelstraat) there's a very cute French placed called Le Zinc, where you can customize a daily tasting menu by choosing from 3 to 5 courses, and add wine paired with each course. You can then sit in the corner and watch people make a$$es out of themselves thanks to the over-abundant wine. (That would be me. )