My personal favorite is the Raven Phantom. A great design that is both an inside and outside the waistband holster; you simply change the belt loops. Well worth looking into. they have a good backlog but they are well worth it. I really like the simple Glock Sport/Combat holster and I've used one for going on 3 years as a daily carry holster and an IDPA competition holster. Both Comp-Tac and Blade-Tech make great holsters, too. Don't go on the cheap; you just dropped over $500 on a good gun don't balk at spending 20% of that cost on a home for it!
I purchased a Clipdraw for my Glock 27.
Mounts on either side of gun. No holster required. An option to consider for about $25.
May not be the end all but you can always tuck your gun away.
What holster do you all recommend for a glock 21?
What holster do you all recommend for a glock 21?