If you have to do complex layouts on lots of pages, YUI Grids are very powerful and will save you a lot of time. Layout Gala has some nice CSS layout templates for more basic layouts, they make a good starting point. I'm curious to try Blueprint, mostly because of the sweet baseline alignment, but it was a little limited last I checked.
For me a reset file is essential, Eric Meyer has one, Blueprint has one, YUI has one... I really like the YUI reset-fonts-grids file because it standardizes font sizes across browsers and makes font styling much more predictable and controllable. And I like the YUI reset. Even if YUI Grids are overkill for your project, the reset and fonts stylesheets are handy.
I typically use pvii's CSS Layout Magic as my base starting point. The code is lean, and compliant, and caters for all sorts of layouts - fixed, fluid, 1,2,3 cols - just great. Course, by the end of it, I'm not sure they would agree with the mods I end up doing to it ;-)
Interesting, I haven't looked at PVII's stuff in awhile, I will have to check it out. One product I thought looked interesting, to aid in building CSS layouts, is WebAssist's CSS Sculptor:
Hi, I have this extension with Dreamweaver CS3 - it is a very nice product, easy to use. The results are pretty solid. Dreamweaver also has pretty much the same starting css templates but the Webassist one does let you save any settings and modifications, so over time you can build up any variation of a starting design and just tweak the settings for colours, fonts etc each time.
Hope this helps.