nice hotel in amsterdam...?

near the city center if possible...

Try the Tulip Inn, it's nice and clean and moderately priced. It is located on the Dam Square, in the center of Amsterdam.

http://en.venere.com/hotels_amsterdam/nieuwe_zijde/hotel_tulip_inn_dam_square.html

NH Amsterdam Centre

Stadhouderskade, 7 1054ES Amsterdam, Amsterdam
Tel. +31.20.6851351
Fax. +31.20.6851611
nhamsterdamcentre@nh-hotels.com

In the city's cultural centre, overlooking the Leidseplein, the hotel enjoys an exceptional location, surrounded by theatres, museums, nightclubs, luxury shops and many cafes and restaurants. It is found only 10 minutes from the Convention centre (RAI) and only 15 kilometres from the Airport of Amsterdam-Schiphol.

Good luck!