Most titanium frame-locks are satisfying to open/close, especially Kershaw's assisted frame locks. I really like my Spyderco Military in titanium, as you have the added fun of the Spydie drop. Axis locks are fun, as mentioned above, when you have the tension just right, and flip it open and closed, and get it timed perfectly. I miss my BM 42, as it was great. If you have a chance, a double-action (or is it dual action?) automatic side-opener is fun, as there are 2 ways to open it. And nothing beats the fun (and workout) of a double-action Out The Front auto with a hard spring.