Lunch within walking distance to Beale St.
If your wife's not big on bbq, I'd skip Rendezvous - the grilled chicken is not going to be anything amazing. The ribs can also be a little hit or miss. Some people love them, some people hate them. I've had good and bad ribs there.
There's a good cajun/creole place on Beale St. called Johnny G's.
Majestic on Main Street is very good.
You could take the trolley down Main St. a few blocks and then walk one block over to Front and eat at Gus's Fried Chicken. You could also walk if you're up for a stroll - it's only a few blocks from Front and Beale, but it would be a bit of a hike. This is probably what I'd do.
Gus's is great and not too far from Beale. There are 4-5 Gus's restaurants around Memphis and they are all essentially the same -- hopefully your wife likes fried chicken because it is some of the best.
if you want something a little more upscale you could check out:
McEwens on Monroe: http://www.mcewensonmonroe.com/
Felicia Suzzane's: http://www.feliciasuzanne.com/
Automatic Slims: http://www.automaticslimsmemphis.com/
I haven't been to lunch at Slims since their new chef took over but I assume, like the dinner, it is good.
They are all a few blocks from Beale. Majestic is good but I've found the service is kind of slow and I think the three places above are about the same price and have better food.
Bardog and Local are both good as well -- they are foodcentric bars
Again, these places are a couple blocks off of Beale -- IMO the food on Beale is pretty lackluster although I haven't been to Johnny G's which is mentioned above
Automatic Slim's Restaurant
83 S 2nd St, Memphis, TN 38103
These are all good rec's, except to klebb's point, I think automatic slim's lunch is very disappointing since the new owner/chef took over. It used to be a really interesting place - now it's mostly sandwiches and it's always empty. I hate to be down on it, because I used to really enjoy it.
Felicia Suzanne is a very nice place and only does lunch on Friday.
Majestic and Felicia both have nice patios - if the weather is as nice as today that would be a plus.
Felicia Suzanne's Restaurant
80 Monroe Ave Ste L1, Memphis, TN 38103