Usually, there is no need of a cleaning software to speed up an Ubuntu machine. There is no registry in Linux and temp files are on /tmp directory which is not saved when you shutdown the machine.

Log files are on /var/log and have absolutely nothing to do with the speed of the machine (while they do not fill up the disk of course). Each log has several files because the old ones are compressed and a new one is created. The compressed (old) ones are usually in the form /var/log/logfilename.#.gz. Usually 2 files of each log are not compressed, the current one and the one before it (usually named logfilename.1). It is not needed and won't speed up your machine but if you need some small extra disk space, you can delete all the compressed ones if you don't need them (sudo rm /var/log/*.gz should work but you may need to do some adaptations depending on the names of your log files).

A few little things you can do manually:

Due to the package management automatic dependencies installations, you may have auto installed package that are not needed anymore. Remove them with: sudo apt-get autoremove

Look at your swap to see if it is used heavily (not enough RAM):

free -m

The last line will tell you swap size, used and free. If use is high and you see on the above line -/+ buffers/cache that free memory is short, you may need to increase your RAM to speed up your machine. If swap is near 100% used, you need to increase swap space (but that is another question :) )

Browsers caches usually can be cleaned from the browser preferences.

Or as suggested in other answers, you can use Ubuntu Tweak! :)