If you want something even more advanced than Packet Tracer (which is an awesome tool nonetheless) research dynamips/dynagen. Its also a Cisco emulator. I've been meaning to set this up but just havent found time time. Heard its great.
I've only used PT before, but I'll look up your suggestion now. TBH though, for a CCNA exam you don't need anything more advanced than Packet Tracer Maybe if you were shooting for your CCIE or something