I like gluing washers to the bases of my mini's. It makes them just a little weightier and a little less likely to tip over. The best stuff I have found for this is Gorilla Glue. When it dries, it forms a tough bond. The best part is that the glue is somewhat rubbery. This means that dropped minis don't lose their bases. This stuff can take a bounce. I have been using the standard stuff that dries a light brownish yellow. I just bought the stuff that dries white and I will let you know how that turns out.
Two things about Gorilla Glue.
1. It works best when under pressure. What that means is you have to be able to clamp it and leave it.
2. It foams as it activates and dries. This produces a good bond, even on uneven surfaces but it leaves some strange results. It is easy to trim off of a base or file down. I have had problems using it in tight detail places as you can't quiet get your files and knives down into them to clear out the small stuff.
I don't recommend it on arms other places where it might foam onto your details but for big flat surfaces, it is the toughest stuff I have found.