Dealing with web frontends, the need of a consistant icon library is crucial. Of course you can use the icons of the SAPUI5 library. But besides this, every SAP ABAP stack also hosts an nice icon library. You can use the following url to have a look at the icons:
A side note about the SAPUI5 icons: if you ever wondered where all those nice icons come from, you should look out for a true type font called “SAP-Icons.ttf”. At first glance, this looks like a regular font file. However, starting with unicode xE000 (57344) there hide all the nice icons. You can make them visible with various tools or simply in Word, where you can use any unicode character by pressing the (decimal) unicode number on the numeric key pad together with the “alt” key.