Do you mean having a 802.3ad channel using ports of different modules, i.e gi3/1 and gi4/1?
If so, are they the same model?
Yes you can setup etherchannel with LACP across different modules within the same chassis on a 6500 subject to the standard provisos about etherchannel port restrictions ie. they must be same speed etc...
You can group ports from different modules within the same device.
Of course the interfaces must run at the same speed as Jon said and one more thing I would like to add is that sometimes the modules have different QoS queuing types then you must disable the following on the port-channel interface:
no mls qos channel consistency
The 3750 switch supports cross stack etherchannel. Thats the switch you need to go for.
Just to clarify though. 802.3ad = LACP and not cross stack etherchannel. So there are cheaper switches that support LACP but not cross stack etherchannel.
802.3ad is LACP (Link Aggregation Control Protocol) which is an IEEE standard for forming etherchannels.
Cross stacked etherchannel can be used on the 3750 switches where the member ports of an etherchannel can be on different members of the stack.
Obviously the 6500 doesn't stack so in normal operation where you have a pair of 6500's connected via a trunk you could not connect a switch via etherchannel to both switches using the the same etherchannel.
But with VSS, the 6500 switches now support MEC (Multichassis etherchannel) which would allow you to connect a switch to a pair of 6500 switches using the same etherchannel.
Would the "Cross Stack" allow me to create one end of the ether channel across the 3750 stack and the other end to an aggregate server connection?
Or do both ends have to be on 3750 stacks?
No, both ends do not need to be on 3750 stacks. So you can use cross stack on one end of the etherchannel on a 3750 stack and then standard etherchannel ie. from a single device, whether that be a switch or a host, on the other end.