Install and update dozens of apps at once
A few years ago my friend Jon pointed me to ninite.com. It's a website that's a one stop shop for the standard geek suite of software covering web browsers, IM's, media players and security to just name a few of the categories.
Personally I pick up all the browsers because they're handed for testing website compatibility. I've been using Trillian as my IM for years. VLC is great for videos and I really didn't have to mess with codecs, codec packs and arcane codec compatibility issues anymore once VLC really hit it's stride. Although it's not on the site, Real Alternative is a handy player for RealMedia files (.rm) although they're not quite so common anymore.
Runtimes
The runtimes are handy, especially on a new install because they're kind of forgettable until you run into the website that requires one. Flash and Java are pretty necessary, Silverlight is used by Netflix and a growing number of content providers and .NET is probably a necessity as well. On a long enough timeline you will probably need Shockwave.
Imaging
Paint.NET and GIMP are great image editing softwares that are a lot nicer than MS Paint and don't cost hundreds of dollars like Photoshop. I have heard that Paint.NET is a little more accessible to novices. Picasa is a nice manager and IrfanView is a great for processing large batches of pictures.
Documents
Gotta reccomend LibreOffice. OpenOffice used to be the alternate office suite of choice when Ms Office wasn't desirable. However issues with Oracle purchasing Sun Microsystems have made OpenOffice's future a little iffy. But LibreOffice picks up where OpenOffice left off so it ought to be OK. LibreOffice also has an estimated 25 million users currently.
Security
I'm currently using MS Essentials and it seems to work pretty well. I have used AVG and Avast over the years as well and never had any complaint. Adaware and Spybot are necessary if you have issues with spyware or have a shared family computer. No matter how smart you are, a shared computer is only as safe as the dumbest user.
Other
Steam is the online standard for digital content distribution. They have great sales and even some decent free games, not mention they recently made Team Fortress 2 free to play. Portal has been given away for free, Alien Swarm is a neat top down squad based alien shooter. There's also a growing number of free to play MMO's if that's your bag.
Compression
I used WinRar for years with no complaints. I like 7-zip better these days though, so if you ask me, 7-zip.