For office stuff I use MS Office as, like others have said, it just works with Windows based MS Office files (ISTR there are some things that are incompatible, like VBScript, if that matters to you). I just got my copy for about a tenner through the MS Home Use Program as work has volume licenses. If you have someone in the house in education, then you can get a pretty cheap fully legal copy from
software4students. Whilst OpenOffice and LibreOffice are good enough to use stand alone, they are not quite ready to use as a drop-in replacement when you are doing interactive working between those and MS Office installations - you'll get driven batty by minor (and sometimes major) formatting issues.
I do have VMWare Fusion installed, I use it for some apps that there aren't Mac versions of (like Visio, or my accounting stuff, which can sit in it's own clean VM with no other software installed) and the Garmin utilities. I sometimes need Ubuntu on my Mac, so VMWare takes care of that too. If you have a Windows license that you can put onto it and a copy of MS Office for Windows then you can run that almost as well as a native Mac version - there is a mode where you don't see the Windows desktop, just the applications running like any other Mac app (except for some funnies in the filesystem, as they see the virtual Windows FS and you have to treat your Mac FS like a network drive). You can still do things like open a Word document from Finder and it will start up your Windows version of MS Word running under Fusion.
Other reasonably general tools I use a lot -
TotalFinder makes it easier to handle files and move them around (allowing things like double panes).
DevonThink Pro for information handling
Skrivener for writing
Postbox for email (Thunderbird based)
Pixelmator for manipulating pictures
As a new mac user it's worth keeping an eye out for "bundles" - every so often a set of useful software will be made available very cheaply - typically around $800 of software for $50. Obviously you'll get filler in these and stuff that is of no use, but occasionally there'll be enough useful software to make it worthwhile (Parallels is often bundled for less than the price of buying the program on its own, for example). A couple of places that keep track of what is on offer
Mac App DealsMacHeist deals around the web