1, Catalyst supports VSS( Virtual Switch System )for combining 2 switches into one logic switch, just like virtual chassis in Juniper EX. While Nexus support VPC (Virtual port-channel) to combine ports from different switches into the same port channel. However 2 Nexus switches with VPC configured still run independently in control plane level, therefore L3 redundancy need to be realized by enabling hsrp or vrrp. Virtual chassis in Juniper will select one switch running as control chassis and the rest of the chassis running as line card in active/passive mode. VSS is very much likely as Virtual chassis in Juniper.
2, Nexus support VDC(virtual switching context ) to separate one switch into several switch logically. VDC will actually run separated control plane for each switching context, that means each VDC has its own L2/L3 instances (vrf, hsrp, lacp, etc)
3, Catalyst support wide range of WAN interfaces and extra FW/VPN modules.
4, FEX support: Nexus 7000 supports the use of the Nexus 2200 Series fabric extenders to additionally expand the system and provide a large-scale virtual chassis in the data center. Up to 32 of the fabric extenders can be supported by the Nexus.
5, Difference between Nexus 7000 and Nexus 9000 is that Nexus support ACI (Application Centric Infrastructure) That will facilitate SDN deployment. There are some other differences too which need to be further researched.