I use
digilabs. The backend software isn't the greatest- but it's definitely not hard- and once you get it all figured out, it's extremely simple.
You have a ton of options, like the ability for customers to compare images side by side (which my clients love- it was their biggest complaint about my old system) they can perview in black and white and sepia (this can be turned off if you don't want it available), and you can create sub-categories. They can also watch all the images in a slideshow (just a basic run of the mill run through) and also create favorites folders or other folders and any of which can be sent to me. I love this cause I use it to ask my clients to send me their top 10 favorites for their album. Comes right into my inbox without having to ask for numbers or writting emails, etc.
You can also set all your own color schemes and put your logo on top.
Here's a link to one of my galleries with categories if you wanted to check it out from the customer side, and I believe you can see a few on the digilabs website too.
Hope that helps!