I came across Artspring about a week ago and signed up for a free trial. Love the user interface. It's so easy to use.
What I love most is that it includes a full art inventory database, not just a portfolio website. This means I don't need 2 different services. It's all in one.
But it doesn't stop there either. You also get contact database, email newsletter system and a way to track all interactions with your contacts. So like a CRM.
The art website themes are clean and professional and easily customised. With full access to the site files you can even get your own designer in to do a complete custom design!!