I don't really bother with any third-party cleaning applications and defragmenters. Most of the time, the tools that come with modern versions of Windows should more than suffice, and they might even do some extra things. (For example, Windows' own defragmenter knows about application prefetching and other things that Windows uses to keep track of application launches and data usage, and optimizes the drive layout with locality of data in mind. Take an application that reads file A, then a bit of file B, then file C, and then another part of file B as part of application startup. A really smart defragmenter would know how to lay out these files together... and intentionally fragment file B to make sure that a HDD reading data files for said application won't need to seek.)
Windows can also spot-fix NTFS volumes since Windows Vista (though it's significantly improved in 8), and NTFS is itself a journaling file system. Only in rare cases should a CHKDSK be necessary for file system consistency. (Note that a journaling file system will do nothing to any data loss caused by said file write being incomplete unless VSS/Transactional NTFS is being used. (Yes, NTFS has limited copy-on-write support. Not bad for an "old" file system, eh?)) (VSS also makes it possible to create a system image of a running system while it's in use.)
Long story short: you don't need to take much care of your PC these days. As long as you're running an up-to-date antimalware solution, you should be good.
Of course, having too many apps on startup can slow a PC down during boot - for that, I use Sysinternals' Autoruns. (Windows 8's own Task Manager also works.) (Also note that Sysinternals is technically under Microsoft.)