A Netgear DG834PN, with DGTeam firmware is probably the most stable and tweakable router I've got, I've got a Belkin 7633 [from a few years back] which is very very reliable now I've firmware updated it to the beta (before it was an unreliable buggy POS) but its not quite as flexible as the Netgear.
I've got the Billion 5200G with the 6db forced SNR firmware as well, thats exceedingly fast, but cant hold onto my line reliably in the same way the Netgear does (although becuase of a silly target SNR right now, I can only FORCE my SNR down to 9dB right now with the Netgear, with the target SNR in the DGTeam firmware down to 1%!)
I've seen the Belkin cheap enough though (from OcUK a few weeks ago) that as long as you're ready to check the firmware and BETA it if need be, it might be a good shot if you can find one. OcUK do the DG834PN pretty cheaply too.