Q:

How to give some boost to some really good answers that arrive late?

It happens sometimes to receive or see a very good answer that arrives very late and that would deserve more upvotes.
What can be done to give a boost to them? I would happily spend some of my reputation points to be able to give them such boost.
This is not merely a question of reputation but the idea is to let the answer "bubble up" faster so that it can be seen easily by other people to look into question.
I hope I explained my question so that is understandable.
EDIT 1: I set a bounty because I would like to have more opinions about this issue.
EDIT 2: Bounty time is running out, I have to choose an answer but I am not convinced too much.
Most of you got the point and there are some interesting proposals like the one that proposes to put randomly an answer at top. But I have not enough experience to say if there is one that could solve the issue or not. I would be curious to know what Jeff thinks about it, if it feels there is something that can be improved or not.

A:

Usually an upvote with a comment along the lines of "+1 this answer is very good because so-and-so" will be enough to entice other people to vote it up. There's not much else you can do, really.
If you feel really strongly about an answer being very good and feel the user hasn't gotten the reputation he deserves, people sometimes go through the user's profile looking for other (good) answers to upvote them as well. Doing this too much will probably get you flagged and will end up hurting the user, though.

A:

Supervotes!
(Now raised as a separate feature-request: Should we have a small number of Supervotes per day?)
Something I've thought might be a good idea would be to give each user a small number of Supervotes per day.  These would be worth several normal votes, would possibly cost some rep, and would be rationed to maybe 3 per day (as opposed to the 30(?) per day limit for normal votes).
Sometimes you see answers that are so good you want to upvote them really hard.  This would be a way to do it.
But of course it complicates the voting system, and the UI, and probably isn't worth the costs.

A:

There are several options that have not been discussed:

Display answers with the same vote total in random order. Example, if there are 30 answers with a score of 0 you may not read through all of them so give each one a chance to appear at the top of the list of '0' answers.  That way the system isn't arbitrarily pushing a low-score over a higher-scoring answer but newer answers don't languish at the end of the list.
Save a display slot on the first page for a random answer with a low score.  Give it a different colored background to distinguish it from the standard sorted answers. 
Sort answers of the same score by order of the reputation of the answerer. The downside here is newer users would be somewhat penalized solely for being new.  That being said, rep is supposed to mean something.  Another side-effect is that high-rep users would get more views for even their less-serious answers.

