Everybody using VS should already know about Resharper. But just in case someone doesn't - this is a must to have if you work for enterprise, request it from your employer now!
Resharper slows VS down immensely and adds way too much cruft in my opinion.
If its slowing your machine down, there's a few things you can do like turn off code analysis which will help, you can optionally run this later.
As for the additional things it "adds", there's pretty much an option to enable/disable/customise everything.