Don't know about weed growth, but marigolds are naturally pest resistant.

There are many great companion plants/flowers you can put between your garden delights. It just depends on what you are veggies you are planting and what companions go with them!
A really good book (you can probably find it just about anywhere) is Jerry Baker's 'Impatient Gardner' (haha on the name too). He lays out some lists of good companion plantings dependant on what you have growing. Hope this helps!