Hi,
There's plenty to do in winter/spring round Liege.
Freyr is the best area by far. About an hours drive from Liege. The routes on the 5 Anes and Al Legne sectors are very, very good. Have a look at the Belclimb routes-db for to get a idea which routes are best. There's good climbing in Mozet, Beez, and some smaller area's near the river Meuse as well.
The crags along the Ourthe river tend to be small in size as well in the amount of routes. Like slabs? Visit Esneux, Tilff or Les Awirs. Fancy bouldery routes - indoor style: Bomal is the place to go. Cobblestone: Roche a Frene.
Like cracks and/or trad? Go visit Ettringen! About 1:45 from Liege and located near Koblenz in Germany. There's about 1300 routes to choose from. The website klettern-Ettringen.de has got a list of all the routes. It's a good place to visit in winter as well - we'll go there on sunday and with the current temperatures and a bit of sunshine I expect to be able to climb in a tee without being (too) cold.
Indoors there's plenty to choose from as well: Liege, Heerlen, Gulpen, Aachen, etc. There will be a large bouldering gym in Sittard in 3 months time.
Berdorf in Luxembourg has some great climbing, but the crags need some time to dry after the rain of the past weeks. Beware of condensation in winter after a distinct rise in temperature. On a good day in winter or early spring nothing beats climbing in Berdorf - well, maybe climbing on the Al Legne...
Have fun!