You can also modify any FOP to accept an 80mm fan. Just buy a FOP and your 80mm of choice. If you really want high performance, the YS Tech 80mm High Output can move something like 47 cfm at 39 dbls (not that quiet, IMO). If you're after true quietness though, you can go with the Panaflo 80mm for 39 cfm at 32 dbls.
If you already have the LOUD delta fan don't scrap it for a quieter one. Just add a rheostat in the power line to the fan so you can adjust it to your liking. This will cost like 2-3 bucks at rad-shack.