I've been in Santa Fe for 3 months for business and have eatten our a lot. Below are my favorites.

La Boca (1/2 off at Happy Hour from 3:00 to 5:00) - Get the Blood orange sangria
Restaurant Martin (has outside dinning)
Jambo
Pasquales for Brunch

Favorite for New Mexican is Maria's and they take reservations.

I've spent the past few months in Santa Fe on business and I'm a solo diner most of the time and have found that most restaurants are accommodating, as well as vegetarian friendly, though below are some or my favorites for eating alone

Recommend: La Boca (my favorite restaurant in SF), Pasquals (community table), Outdoor patios are great - La Posada Hotel, Inn at Anasazi (patio or bar), Jambon (great food African / Caribean (bar and 2 community tables), Vinaigrette (salads), Shibumi (as someone already suggested (I sit at the equivalent of a sushi bar and watch the chefs cook. they are always nice to me when I dine there), The Tea House on Canyon Road

Good Luck and have fun dinning