Oh I sympathize! I have to laugh when magazine etc recommend carrot sticks and the like as a healthy snack - er no!! Not going to fill the gap.
Things I find that help - as Skinheadmermaid said, exercise is great if you can find something you enjoy. If you can head out for a run after work then you may find you don't need that snack after all. You might think, I can't exercise, I'm starving, but it is actually just an energy slump and the exercise is just what you need to invigorate yourself. It also gives you a buzz and makes you feel more positive about yourself.
On a similar note, looking after your appearance in other ways, such as wearing nice clothes, styling your hair, makes you value yourself more and feel more in control of your appearance, which really helps with making healthy nutritional choices, or so I find. I battle with low self esteem and depression and this really helps me. It is akin to the thing about prisoners of war who stopped shaving being the first to die as they had given up on themselves (don't ask me where I read that, maybe Primo Levi, maybe Hello magazine 
).
If you need a snack after work you can either borrow something from your dinner, e.g. have some toast after work and then skip the potatoes/pasta/rice with dinner, or else if you want something sugary just go with it and have a biscuit and a cup of tea when you get in, but make that your treat for the day. One chocolate biscuit won't make you put on weight if the rest of your diet is good, and a bit of chocolate each day is more manageable long term than a diet without treats.