Contribution valuation options

I would like more options when valuing contributions. Ideally, I would like to be able to manually enter an integer dollar amount.

If we were to keep the fixed valuation options how many more options do you feel we should have? They are currently:

0, 5, 10, 20, 40, 70, 100, 150, 250, 400

I think there may be some benefit to having these distinct levels, although I'm not sure about that. The other option is to have a one-click sliding scale that goes from 0-500. Basically, as you mouse-over it would show you the amount you're valuing the comment at. This scale could be logarithmic if it helps ease of use.