You mean schematics of operons? Depending on what exactly you want, I'd suggest SnapGene (if you want to do it 'by hand' with a great deal of customisation and ease), or EasyFig (usually used for alignments though), There's always the option of just making a screenshot of Artemis, JBrowse, IGV and any other genome viewer, if you have a genbank file. You'll need to give us a bit more to go on or an example figure you're trying to emulate before we can give you an exact answer.

And last (and definitely least), a lot of people I know, mainly less tech savvy PIs, will just draw it with boxes and arrows in powerpoint! (I absolutely do not endorse this :P )