You can use www.hrs.com to search and book a hotel in Wiesbaden and/or Mainz.

I stayed at the Radisson SAS (Schwarzer Bock) so far and really liked it (very good and well-known restaurant). There's also the Nassauer Hof. The Nassauer Hof is one of the best restaurants in Germany ("Leading hotel of the world" - member) and I can highly recommend it: a hotel with a rich tradition and grand style.

You can good (weekend) rates for these hotels on www.hrs.com .

edited to add: both hotels are central. You can go there by S-Bahn and then
a) by taxi 5-10min
b) by bus (the price for the bus ticket is included in the S-Bahn ticket). The bus stops near both hotels.

[This message has been edited by LH738 (edited 04-09-2003).]