Every consignment store I've ever been to WILL take work clothes - suits, blouses, etc. I've never seen one that will only sell designer clothes. They've all been willing to take Banana Republic, Ralph Lauren (not the couture stuff, but the more casual stuff), White House Black Market, that kind of thing. Most of these places have the clothing divided into sections: cocktail dresses in one area, work suits in another, sun dresses, and so on. Have you been told your clothing is not suitable for consignment? If not, I'd try it. If one place won't take them (because they only specialize in a different type of clothing, or are looking for different sizes, maybe), ask them if they know of a store that would take that type of clothing.
If all else fails, you can always donate the clothing to a women's or family shelter. In our area, there's a shelter for abused women who are trying to get back on their feet, and this shelter is always looking for clothing that women can wear to interviews. A lot of the women literally have to leave everything they own behind, and so they have nothing to wear when they're interviewing for jobs. No, you wouldn't get money for it, but it's tax-deductible and would make a positive difference in someone's life. Just a thought!