First off, if you haven't signed up for their CVB's coupons, I'd do that!
http://www.visitsanantonio.com/visitors/save/index.aspx
Ideas:
The Alamo is the traditional tourist mecca...and we go every time we are in SA...but IMO, the other
missions in San Antonio are better.
Six Flags Fiesta Texas will be open on weekends and during spring break in March.
The Zoo and Brackenridge Park
The outlet mall in San Marcos...love it! We hit the Disney Outlet, Crocs, and hubby goes for the tool stores.
There are a lot of caverns in the area. Natural Bridge also has a wildlife park...it's one of those drive-thru types if I recall correctly (it's been awhile)
Dinosaur Quest might be popular with the kids...DD is just getting into dinosaurs so it's on our list of places to go next visit.
There is a Texas Ranger Museum near the Alamo...but honestly, we felt it was a rip-off. Very pricey tourist trap (most things near the Alamo could fit in this category IMO). The Ranger Museum in Waco is at least as nice and much cheaper. The Dr Pepper Museum is also in Waco and DH enjoys stopping there to get the cane sugar Dr Pepper from their gift shop.
As far as restaurants go, there are tons of good Tex-Mex places...our favorite was Rita's on the River...the BEST fajitas I've ever had.
We also enjoyed browing
El Mercado...just because it's so different from our normal shopping experience.