I've used Thunderbird. The early builds (0.1, iirc) were great, but I had some problems with 0.2+, so I haven't touched it since.
That said, its built in spamblocker worked nearly perfectly for me, and I'm planning on installing it again, once some of the kinks are ironed out.
That said, its built in spamblocker worked nearly perfectly for me, and I'm planning on installing it again, once some of the kinks are ironed out.