Joe, although I do agree with the guys that you'll likely have to cut some more fat before you see abs clearly, I think that what you should do for abs is look at things in a more long term view. You need to work them hard while you are bulking. Next time you bulk, add in some deadlifts if you can do them, start doing some heavy weighted situps, crunches or whatever, and really work on getting your whole midsection to be very strong.
Just keep in mind that you could possibly go too far with the ab training. A good example is quadancer or myself. I think both of us have difficulties with protruding bellies even when at fairly low (relatively speaking) bodyfat percentages, due to large abs that stick way out. You can see this in some of quads pictures where you can see abs yet his stomach sticks out. That's how mine is too. I think I've posted a couple pictures that illustrate this but I don't remember what threads. It's kind of annoying actually.
I am not sure if that is due to training or genetics... I guess it could also be due to a lot of visceral fat, I don't know. I guess I could ask quad if he feels that he has a lot of visceral fat, and maybe that would be the answer to why my belly is distended even when I am at 10% or lower, because I know it definitely isn't GH gut. Haha.
So... at least you don't have that problem, right?
Also, just because your arms, back, legs chest, etc are defined doesn't mean you are at a low enough bodyfat % to see abs. Everyone stores fat differently. I know that my arms are almost always very well defined even when I am at 15% and have a gut... Although for me, it's lower back, quads and glutes that are last to come through, so you just have to figure out how it works for you. My abs are slightly visible even at 15% but my lower back looks like total crap around that level. It looks like you are a little different. It's hard to tell since you only have a front on shot, but I don't see huge love handles or anything... So you can't be too far off from getting more ab definition. Any idea on what your fat storage patterns are like, just out of curiousity?
So don't stress about it too much. You look good, and it's clear that you work out. I think that if you really wanted to get the abs now, you could keep cutting and lose another 10 pounds or so without shrinking away or anything, as long as you do it slowly.
One last thing - were you flexing your abs in that picture? It doesn't look like it. I think you should take another picture, really flex the abs and get some lighting that is more overhead rather than ambient lighting. I bet it will look a lot different.
Also, how bout a back shot? You seem to have a decent V taper, so you've got to have some good lat development.