What's a good web framework and/or tool for a software developer?
It really depends on a couple things:

What are you familiar with?  You indicated that you've done some web development in the past.  What did you use?  If you were using classic ASP, then learning ASP.NET should be less of a jump for you.
What are you trying to create?  If all you need are static HTML files with a tiny bit of functionality, you could try learning PHP as it's pretty quick and easy to get going.  If you need light database access, then maybe Ruby on Rails will be your cup of tea.

With that being said, I'd recommend the following in no particular order (just because I've tried them and they're all pretty decent):

Ruby on Rails
ASP.NET / ASP.NET MVC
PHP
I'd like to make a website, it's not a huge project, but I'm a bit out of the web design loop.  The last time I made a website was probably around 2002.  I figure the web frameworks and tools have come a ways since then.  It's mostly the design aspect that I'd like it to make easier.  I can do the backend language in any language.
My question is:
What are some tools or web frameworks that make the design aspect of making a website easier.  It could be a framework in php/python/ruby.
As far as tools go, free/open source is preferred, but I wouldn't mind looking at good commercial alternatives.