I agree with
@hwmpg...any of the culinary herbs are great.
But plan on all of the seasons. It's easy enough to get stuff to flower mid season, but keep a special eye on VERY early and VERY late. On the late side, you can't go wrong with Tithonia spp. (Mexican sunflower). They start flowering mind summer and go all the way to frost. Any of the large Salvia (guarantica group), and medium salvias will flower to frost as well. Early stuff - consider bulbs and things that grow well with the possibility of lower temps. Snapdragons help. Sedums both tall and low have flowering periods conducive to planning for full seasons (early-mid-late). Consider staggering various Heuchera spp. and cultivars (coral bells) the same way, you can extend the season for smaller pollinators by planning for blooming periods (and colors of foliage and flowers don't hurt either). Coral bells flower for a long time as well. Basically, you don't need to do it all at once. Just keep chipping away at adding habitat structure and you should be better every year.
Lastly, there is a LOT of sales literature on seed packets, websites, etc that say various plants are good pollinator plants. A lot of them aren't...sometimes at all, others may not be in some locations. Don't be in a hurry to fill gaps and do a LOT of looking up species/cultivars before adding them or you'll have several plants that while decent, really may not function like you thought. Additionally, there is a good reason to check on invasiveness before planting. You don't want to compound problems for you or your neighbors down the road.
