The Shimano hierarchy from the early 2000's - Dura Ace, Ultegra, 105, Tiagra.
Generally, but not always, the technology is trickle down so that the stuff from one year is roughly equivalent to the next level stuff from a couple of years before. Ultegra is good but hard to say if you should replace your Tiagra with it. If it doesn't cost too much and you're not happy with the Tiagra, maybe so.