ST-2400 is current model 8-speed by Shimano; and ST-2300 8-speed still popular too. These are what you want - I doubt you'll even notice a performance difference; probably even an improvement with the age of your DA brifters.

The 2300's can be found on eBay for under $40 new if you keep an eye out (and don't mind thumb triggers). Otherwise you can buy the 2400's for around $75-100 new.

Shimano also still makes an HG50 8-speed road cassette.