We are using haproxy in TCP mode for round-robin with great succes.
It's bit unorthodox but has same real added values like logging.
Here is the relavant config for haproxy:
#####
global
log 127.0.0.1 local0
log 127.0.0.1 local1 notice
maxconn 4096
user haproxy
group haproxy
daemon
defaults
log global
mode tcp
maxconn 2000
contimeout 5000
clitimeout 50000
srvtimeout 50000
listen cassandra 0.0.0.0:9160
balance roundrobin
server db1 ec2-XXX.compute-1.amazonaws.com:9160 check observe layer4
server db2 ec2-YYY.compute-1.amazonaws.com:9160 check observe layer4
server db3 ec2-ZZZ.compute-1.amazonaws.com:9160 check observe layer4
