Hi! Wandering by from the friending meme (hooray Northern California and Star Trek and meta and music), and the comfiest sandals I have ever owned are my Keen "Commuter" sandals. I got them originally because I wanted something I could bike in that was still open-enough to feel the summer breeze on my feet, yet not have my feet so exposed that they were likely to get caught somewhere inconvenient, and be reasonably practical for walking around when I got to where I was going. They are awesome. They have toe-bumpers so that I don't stub my toes when wearing them; they have really supportive soles, and they just stay in place without going anywhere (which I can't say for other sandals I've had, even the year I lived in Birkenstocks).

Keens are expensive at retail, but it's worth looking around online for them; 6pm.com usually carries a selection at discount.

Also, one of my favorite shoe blogs, Barking Dog Shoes, talks about comfortable-yet-cute shoes - the writer, Kirsten, has rheumatoid arthritis, and takes reader questions about "this is my situation with my feet, and I need shoes I can teach in/go to a wedding in/walk my dog in," so if you don't end up liking Keens, she's got a whole other list of options that might work. Good luck!