An engineering professor at York came up with quite a nice idea, which was to keep the Commons with the First Past the Post system, and then to radically reshape the House of Lords. The Lords would be reconstituted after every general election (and by-election) such that the total makeup of parliament (MPs+Peers) was proportional to the total number of votes cast for each party. Peers would be selected from a party list system. He also pointed out that this system could also allow the Lords to be used to adjust for demographics, too - ensuring that parliament was representative of the nation in terms of gender, race, etc.
That's actually the best suggestion for PR and the Lords I think I've heard. :) The demographic adjustment is an interesting one, although at that point the argument would become which demographics need representing.

Sex, Race, Wealth, Job/Profession, Sexuality, Religion, Able bodied / Disabled, Home Owner / Renter, Parent / Child-free, everyone will want their own nieche / subculture / special interest to be given consideration.

At what point does it stop being a demographic and start being a choice which is represented via your vote, I guess. No doubt we'd just get bored talking about it rather than actually implement anything, much like Blair's reform of the Lords.
That may have the result, mind you, of landing the BNP in the Lords which is a rather disconcerting result. :/