I thought I would finally touch on this once again; It's been a while since I've done a run down of good alternatives for standard Windows software.
Alright down to business. First off, I don't consider myself an expert on this, so take it as it is. It works for me and many others, some of these are almost mandatory, if you want your Windows system to run better, without any major bloat weighing on it. This is my personal list; it is what I use on a regular basis and have found they work much better in my opinion. I will list a few others that have been recommended by trusted sources.

Alternatives to Microsoft Office:

• OpenOffice This isn't the one I use but I have used it in the past and it's a real nice one to have. It comes with word processor, spreadsheet, presentation , drawing/graphing tool , tool for creating equations and many more.
• LibreOffice My personal favorite and it has the same features as OpenOffice and perhaps more now. I do apologize, I haven't done extensive research on these two but have seen that LibreOffice has gotten major attention; many say it has surpassed OpenOffice. I'm sure whichever choose will be more than adequate for your needs. Highly recommended

Alternatives to Adobe Photoshop:

• Gimp I love this graphics editor, 100% free with free lifetime updates, multiplatform support, small footprint so it's easy on resources. Also has paint brush, pencil, airbrush, erase,  ink tools, fill, clone, layers, channels, automation, scripts and plug-ins. Simply awesome. Highly recommended

Alternatives to Adobe Reader:

• Foxit Reader The one I currently use and it works great, I haven't had any issues, however, some have stated that Adobe Reader alternatives sometimes had issues displaying certain PDF files correctly. But again, I have yet to experience any problems thus far and I've been using for quite some time now.
• SumatraPDF I haven't used this myself but have heard it's a great alternative also, so if you decide to go with it, I'm sure it will work just fine for most needs.

Alternatives to Antivirus suites:

•  Microsoft Security Essentials  I don't use this anymore, but that's not to say it didn't work well, just personal preference. I still highly recommend it as it's easy on resources, good at catching viruses, and does all of its work in the background without the nagging of some others. 
• avast! Free Antivirus: Some may consider this choice a bit odd, considering there are others with perhaps more features but I simply love it. I've been using this for a long time and it has done me right. I haven't had a bad virus in years(Knocks on wood).

Alternatives to Internet Explorer:

• Google Chrome Very speedy, secure and all around great browser. Not my first choice but I do use it and quite often.  
• Firefox My first choice, as I've used it for as long as I can remember, I've been very faithful to Firefox and again, this is just my preference. Both this and Chrome are excellent browsers.

 Alternatives for Windows Media Player:
 I'm gonna be honest here; I do still use WMP, just not very often at all. It just lacks support in so many ways and you need codecs galore to get it to work right sometimes.

• VLC Player I love this player, it plays most everything I throw at and it has a great interface.
• KMP Player Another I use often, also recommended.

These also make good alternatives for Quicktime

Some other alternatives you might wanna take a look at below.