I currently have a Sony HVL-10DW2 Video Top Light (as previously used on my Sony Fx1) which provides a huge amount of light (10w/20w) but this is often too bright (even with a diffuser over the front).

Does anyone have any recommendations for lights with dimmer switches?

Anyone. Just need something I can ideally mount on the 7d?

Tim, just put some ND, frost or spun on it and you're good to go. There's nothing wrong with your light, it's not that powerful, it just needs the right modifier for the situation. Spend your hard earned on something else:)