It seems that we may soon be heading towards an elected second chamber (replacing the current House of Lords). The problem with an elected chamber is, of course, that it potentially threatens the mandate of the Commons if there is a conflict between the two.
One way round this is to have the two elected on a different basis - for instance, in the US the Senate is elected on the basis of two senators per state, rather than being proportioned to population as the House of Representatives (their lower chamber) is. This provides some protection for the rights of small states, but also ensures it doesn't present a serious rival to the lower house's claim to represent the people. In the UK, it seems that the second chamber could be elected on longer terms and by proportional representation (though I think that may be dangerous if it led to them being seen as more legitimate).
In any case, there is another alternative - we could use sortition (random selection) to achieve a representative sample of 'people's peers'. Proposals along these lines are outlined here and here. I'm not sure whether I'm in favour of this all things considered, but I think it's certainly a shame that it seems to have been neglected in public debate. In light of such possibilities, Lord Adonis' claim that election is "the only way that a legislative assembly can be legitimate in the modern world" seems far from obvious.