This is a declaration of love and shameless plug for the Firebrick FB2500 and FB2700 routers. See firebrick.co.uk website. There's a lot around on the Andrews & Arnold support wiki too.
This IPv6 and IPv4 ethernet router has four ethernet ports on it, is a flexible firewall and has all the usual router functions in two software variants, standard basic version and the “fully loaded” version. My FB2500 is the fully loaded version because I needed to get the load sharing/bonding capability which is part of the top price version and performs outbound load sharing across three DSL modems (unequal speeds too, for some reason, which is a pain as it requires psychic powers to guess what the correct load split should be in the config to get it right for the lines’ link speeds, which could change for all I know).
The functions of the ethernet ports are software configurable, I use three ports for WAN pipes to DSL modems over PPPoE. Supports MTU/MRU 1508-8=1500. So I get three lines inbound IP which is merged together and then understood by the firewall function just as simply as if I had only a single line. Andrews and Arnold are load-spreading even single TCP connections across my three lines, in the right speed ratio too, the firebrick knows nothing about this.
It is an excellent DHCP server and a solid IPv6 router, although I don't fully understand it's DHCPv6 abilities if indeed there are any. It can do NAT and DNS relay/proxy caching. Mine uses a suitable-sized IPv4 address block so no NAT (shudders).
One of the things I love most is its XML config files, so clean and logical. They can be uploaded and downloaded using http, either by hand in the router’s web UI or using appropriate curl commands.
It has (optional auto) software updating over the internet, which is simply zero hassle.
I could do with better, longer documentation for very stupid people like me.
There are a couple of features I could wish for: much more sophisticated QoS being one, DHCPv6 being sorted out or documented, fancier IPv6 address association and management generally, rules and associations by mac address and named mac address groups including mappings from IPv6 addresses from mac to make IPv6 wandering addresses as easy to manage as IPv4 under DHCP locked assignments.
The FB2700 is definitely the one to go for, I should possibly have bought this top of the range device. It's faster and users with _bonded_ FTTx lines will certainly need the CPU performance. It also has a 3G (and 4G?) dongle interface which the lower model lacks. It can failover to this 3G interface, I'm not sure what else it can do with it.
There are rumours about faster new models on the way, which will be the way you need to go if you want to start bonding a load of 330Mbps FTTP pipes together, but then you'd soon need something faster than a single ethernet NIC to get it all out onto your LAN plus some scary switch and posh NICs all round on your machines everywhere.