But, if that's too hard to implement, yes the next best thing would be to have them reset at regular intervals. Once a month seems OK to me (but really I would still prefer to be able to jump between "daily, weekly, monthly, all"!)
I'm not too keen on a randomized list, at least not as the "primary" mode. It's nice to be able to see what people are gravitating towards, what they're interested in, what they think is worth spending time to read, etc.
In my suggestion above, a random feature could be added in for those that want to use it, though. Maybe have it take the top 100 based on "total views", and randomize them. But I dunno, it's not too hard to scroll through the top 100 anyway. Anything beyond that might be a little more difficult to randomize .... there are probably thousands of blogs and I would think generating random lists out of "all blogs possible" for so many people, would consume resources pretty fast.