I agree with Pinky, start at the beginning.
You can't start off with pikes and jack knifes, with the tough core work from the Hardcore series!!! That will just depress you and make you give up on the spot!
Abs/core work is not my fave thing either. It always comes at the end and I often just blow it off. But, when I work at it, I see results very quickly.
I invested in Ab Hits and worked my way through it steadily. About half of it is traditional abs, things you will be familiar with. I particularly like the set from MIS. I try to work the abs/core about 4 times per week. Once this became easier, I graduated up to include the planks exercises, also featured on the Ab Hits DVD. I actually like planks a lot. I don't think of "oh-my-god-how-long-do-I-have-to-keep-this-up?", rather I psyche myself through it by counting in sets of 8, so I reach mini achievements throughout the time. You can get strong with planks quickly.
After this, try the core work from the Intensity series. It is fabulous and very varied, especially the series from Boot Camp, PUB and C&W. There are always some exercises I loathe, others that I just can't feel them doing anything for me. So, I sub it with another exercise that targets the same area of the core muscles, but is an exercise I like.
Don't forget your running is also working your abs. You are just so used to it, you no longer feel it. But you are probably slim, most runners are, so results from ab/core work will show quickly on you. Once you start seeing results and can feel yourself getting stronger, this achievement on its own works to inspire you to achieve a higher level of strength and ability. I have found this to be true for me.
It really is worth strengthening your core. It includes the back muscles and maintaining a strong back now will keep you free from the back pain that seems to target so many people. Also, it will increase your stability in all exercises you do, including cardio. I believe also, that a strong core and upper body are also essential for runners, to help you keep going for longer. Perhaps someone else can chime in here with more information on this.
Challenge yourself with this. What have you got to lose? Not a lot, but an incredible amount to gain. Off you go!!
Clare