As for cleaning, Macs don't need that. Macs maintain themselves quite well. Cache cleaning should be a troubleshooting step only, and note that in all the years I've been using Mac OS X (since 10.1), I've never needed to do it. Don't pay for software that does stuff like this that you don't need to do.
One thing I do recommend is to use Disk Utility (in /Applications/Utilities) to repair permissions and verify the drive before installing any system updates.
* Disclaimer: links to my pages may give me compensation, and should not be taken as endorsement of my services by Apple.
Generally, there should be no need to run anti-malware software unless you are in an enterprise environment. There are no extant viruses affecting OS X. There are a couple of trojans but you would have to be careless and download them explicitly from strange websites.
MacCleaner is maintenance software that you do not need. Most if any maintenance you can perform with more reliable software that is either free or much less expensive and not as intrusive as MacCleaner. See:
Kappy's Personal Suggestions for OS X Maintenance
For disk repairs use Disk Utility. For situations DU cannot handle the best third-party utilities are: Disk Warrior; DW only fixes problems with the disk directory, but most disk problems are caused by directory corruption; Disk Warrior 4.x is now Intel Mac compatible. TechTool Pro provides additional repair options including file repair and recovery, system diagnostics, and disk defragmentation. TechTool Pro 4.5.1 or higher are Intel Mac compatible; Drive Genius is similar to TechTool Pro in terms of the various repair services provided. Versions 1.5.1 or later are Intel Mac compatible.
OS X performs certain maintenance functions that are scheduled to occur on a daily, weekly, or monthly period. The maintenance scripts run in the early AM only if the computer is turned on 24/7 (no sleep.) If this isn't the case, then an excellent solution is to download and install a shareware utility such as Macaroni, JAW PseudoAnacron, or Anacron that will automate the maintenance activity regardless of whether the computer is turned off or asleep. Dependence upon third-party utilities to run the periodic maintenance scripts had been significantly reduced in Tiger and Leopard. These utilities have limited or no functionality with Snow Leopard and should not be installed.
OS X automatically defragments files less than 20 MBs in size, so unless you have a disk full of very large files there's little need for defragmenting the hard drive. As for virus protection there are few if any such animals affecting OS X. You can protect the computer easily using the freeware Open Source virus protection software ClamXAV. Personally I would avoid most commercial anti-virus software because of their potential for causing problems.
I would also recommend downloading the shareware utility TinkerTool System that you can use for periodic maintenance such as removing old logfiles and archives, clearing caches, etc. Other utilities are also available such as Onyx, Leopard Cache Cleaner, CockTail, and Xupport, for example.
For emergency repairs install the freeware utility Applejack. If you cannot start up in OS X, you may be able to start in single-user mode from which you can run Applejack to do a whole set of repair and maintenance routines from the commandline. Note that AppleJack 1.5 is required for Leopard. AppleJack 1.6 is compatible with Snow Leopard.
When you install any new system software or updates be sure to repair the hard drive and permissions beforehand. I also recommend booting into safe mode before doing system software updates.
Get an external Firewire drive at least equal in size to the internal hard drive and make (and maintain) a bootable clone/backup. You can make a bootable clone using the Restore option of Disk Utility. You can also make and maintain clones with good backup software. My personal recommendations are (order is not significant):
Visit The XLab FAQs and read the FAQs on maintenance, optimization, virus protection, and backup and restore.
Additional suggestions will be found in Mac Maintenance Quick Assist.
What kind of anti-virus software is best for the Mac?
Antivirus software really isn't necessary as long as you're careful about what and from where you download. If you feel the need, though, the freeware ClamXav should be more than sufficient.
What is this thing called a Mac Cleaner?
Avoid any iteration of Mac Cleaner. There are two different programs of that title. The one from Zeobit is not malware (some people call it "sleazeware" due to Zeobit's misleading and intrusive advertising) but is unnecessary since you can do all the functions, if and when necessary, with free software. The other Mac Cleaner is a scam.
Posting your email address isn't forbidden but it's wise, in any public forum. If you want email replies to your posts, subscribe to the thread.
No routine maintenance is necessary, including such things as deleting caches, repairing permissions, defragmenting, and the like.
Malware protection is built in, for the little good it does. Avoid commercial "anti-virus" products, which are all worse than useless.
The periodic maintenance scripts are vestigial remnants of FreeBSD. It makes not the slightest difference whether they run or not.
What you do need to do is back up your data. You need at least two independent backups, one of which should be off-site at all times.
You also need to keep careful track of what third-party software you install, in case it causes problems. You must know how to uninstall it before you install it. Any software that comes packaged as an installer should also come with an uninstaller, or instructions for uninstallation. If not, don't install it. This doesn't apply to system updates from Apple.
Avoid third-party "disk utilities." You'll never need them if you have adequate backups. In the unlikely event that a volume has directory damage that you can't repair with the built-in Disk Utility, you should consider the drive to have failed. Replace it and restore from backup.