Make my own conditional tags?

I am trying to create two special pages for my blog. One is a ‘best-of’, and the other a central index and archive.

That’s easy enough, but I also need custom conditional tags for both pages. Or at the very least, I need a way to apply conditional formatting without just rewriting everything (the stuid way).

For instance, I need the appropriate tab at the top of the page to light up and cease being a link.

Can anyone advise?