Liefmans Goudenband is top of its class (an oud bruin).
Boon Oude Geuze is nicer imho than Cantillon (another geuze) but both are really good.
Cuvee Rene is another good one.
Rodenbach Grand Cru (a flanders red) is also excellent.
The right kriek is very nice. Avoid Lindemans, too sweet. Liefmans do a cherry based beer they used call kriekbier until very recently, again it's excellent. As it's not lambic based they renamed it to Cuvee Brut so you might see it in stores as either.
There are not an awful lot of them, and they're not all good, but you should be able to find something that you like.