Hardware or software? There's some hacks with TPROXY/HAproxy I've seen that would do the transparent proxy but the setup seems like more trouble than it's worth.
IPVS is built-in to the Linux kernel, and HA projects like keepalived have ipvsadm integration. Tproxy works fine, and has been in the kernel since 2.6.30. In most load-balancing cases, losing the remote IP address isn't that big a deal (you have to deal with NAT too), and a full proxy like haproxy has it's benefits.
