Everyone is talking about Barcelona - not the city, the server processor version of AMD's K10 architecture. As Fuad from Fudzilla.com is pointing out, only a fraction of us will invest money in that type of CPUs. So let's talk about the desktop version:
Starting from the Barcelona it sounds very logical that there will be two quad-core desktop versions. The Athlon 64 X4 (2MB shared L3-Cache, codename 'Agena') and the Athlon 64 FX (2MB shared L3, codename 'Agena FX'). There will be a dual-core Athlon 64 X2 ('Kuma'), it's unknown how much cache this will have implemented and last but not least there might be a single-core Athlon 64 ('Rana').
Some of the improvements of the K10 architecture are a faster HyperTransport solution (HT 3.0 up to 4GHz) and improved power saving modes (you don't need a driver anymore for it to work). Both will be supported by the new AM2+ platform. It remains to be seen if the new CPUs will be drop in compatible to existing sockets (losing the HT3 speeds and new Cool'n'Quiet features of course).
Btw.: Fuad is talking about 'Budapest' as well which is a 1xxx Opteron supporting a single socket only.

Update:
After writing this post it came to my attention that there are several more websites knowing something about the K10. In a German forum called Effizienzgurus you will find some more news regarding the whole lineup of processors.