I used to go to Simon's in Lynn. They are nice enough people, and the stuff is cheap, but the turnover time is out of control. Alot of times if you walk in to order a shirt with a little tailoring or a pair of pants with a few extra pockects, you're looking at a week to two week wait for them to call you to tell you they are done. Alot of times they forget to call you too, so you have to chase them.
I go to Neptune's in Haverhill now. It's pricey, but the stuff is top quality, and they tailor your stuff right there for you in one sitting. Just got a pair of pants and a shirt the other day, got measured, tried on, and tailored all in the span of say 45 minutes. It's worth the extra few dollars to me.