There are lots of summer flowering bulbs that should be planted now - dahlias, glads, lilies just to name a few. Also crocosmia, cannas, callas, caladiums and lots of less common bulbs like tigridia, lycoris, acidanthera, etc. Local nurseries and garden centers should carry a selection and one can usually find a more limited selection sold by the home improvement stores and mass merchandizers. If planted now, all should bloom this summer/early fall.

All bulbs are perennial but not all are hardy. A lot of summer flowering bulbs originate from tropical or semi-tropical climates so they are not always winter hardy in the ground. Most should be good in zone 8 but not a guarantee. If not fully hardy, these bulbs will need to be dug in fall and stored over winter.

Thank you! I'll try to go with my mom this weekend or next and see what some local nurseries have to offer.

Looking ahead, are there bulbs that should be planted in summer? What about fall (besides tulips)?

The vast majority of bulbs are either planted in spring for summer/early fall bloom or in fall for spring bloom. There are a huge assortment of fall planted bulbs that will offer late winter through to late spring/early summer color - narcissus (daffodils), hyacinths, tulips, crocus, snowdrops, etc. Virtually all of these will be inground hardy in your zone although some may require a prechilling in your area before planting to bloom well.

There are lists of spring blooming bulbs that are recommended for southern/Texas gardens that include those that will bloom reliably without prechilling.

Here is a link that might be useful: bulbs for southern gardens