There are grass killers that are safe to use in your flower beds, but if you're trying to kill other sorts of weeds without hurting your flowers there's nothing that you can just spray everywhere, you'll have to either hand pull the weeds or spray carefully or paint it on the weeds so that you don't get it on your good plants. On the grass killers, make sure you get one that specifically says it just kills grass, there are a billion things out there that say "grass and weed killer" and those will kill your flowers too. I'm not sure how easy it is to find the "just grass" ones, I have one that's Green Light brand that I found at a local nursery, but it's not something that I see everywhere so you may need to look around or find it online somewhere. Probably only worth looking for it if you've got a huge amount of grassy weeds, otherwise it'll probably be just as easy to get the broad spectrum weed killer and paint it onto the grass weeds as well as the others.
I can't decide whether I'm a believer in mulch or too lazy to weed. (probably a lot of both) When I get a bed ready and put in the plants I want I've found it helpful to sprinkle Preen. It doesn't kill what's rooted but it stops, almost all, new weeds from starting for a short period.
After 2-3 weeks I put down a thin layer of newspaper and add a couple inches of mulch. When I inspect the plants for progress I pluck the small plants I don't want. When I get busy (or lazy) and don't inspect for a while I use a rake or hoe to rough up the mulch and dislodge the weeds.
As long as the weeds don't have too much time to get rooted they pluck easily.
I like the mulch idea. Here in AR where the summers are hot and dry, the beds where I have had time to mulch look much better than the ones that don't have any. The mulch also tends to help hold the moisture and like Adiantium and GK said, the weeds that do root in the mulch are much easier to pull. We have lots of hardwood trees and in the fall when we clear the leaves out, we put them in a large pile, which over time breaks down into nice mulch. I dig down a bit in the pile for my mulch, and as an added bonus, I find loads of earthworms, which go into my beds, too. This is my earthworm relocation program! Most of the leaves are oak which are good for the azaleas.
I try to stay as organic as possible, but I do occasionally hit my garden with Preen when the weeds are seeding heavily just so it doesn't get ahead of me. I also mulch, but I find that the weeds, around here at least, have no problem getting through the mulch. Dandelions, in particular, will laugh at mulch and put down their great bit tap roots anyhow. I get them with a weed picker (small tool with a little fork on the end). The rest I rough up with a little triangular hoe (small enough to get between my plants without damaging anything).
My daylily bed this spring is so overloaded with weeds that I can't even see them. I'm gonna pull as many as I can but I'll never get rid of the johnson grass. If I divide them in the fall is it possible to pick the weed roots out of them? The daylilies are from my Grandmothers garden originally.