URGES...
so we all know urges SUCK!!  i have never found that drawing on my arms or whatever with a marker or food coloring works, but some have so i guess its worth a try.  but here are some other "stuff" to do... good luck :)   also check out "reasons not to kill myself" - great list!!
i would recomend that EVERYONE get a journal... doesn't have to be anything fancy, i get mine at halmark, but you can go to the dollar store and get just a composition note book.  sometimes it really does help to get all your shit out on paper... even if it doesn't stop that urge, sometimes it can help you identify your triggers so that you can avoid them in the future and i LOVE to re read the daily stupid stuff i write down.  i have learend sooo much from my journal entires. 
GET PHYSICAL go for a run, do situps until your belly hurts.  i find that three things become acomplished here... first, im so freekin tired after working out that all i want to do is go to bed.. that gets rid of time to cut.  second, just being outside or out of my apartment is helpful, removes me from the moment.  third, i need to get my body lookin better, i can ALWAYS benifit from sit ups or a run or gym time... plus i feel better afterwards :)
take a hot bath or shower.  baths usually relax me.. i love to load it up with bubbles :) i always think of the dial comercial where the little kid is in the tub and i think the phrase is "wash the world away with dial"... light some aromatherapy candles too, just like in the movies... its so much fun :)  do it when you don't have urges just to pamper yourself. 
call someone... you don't gotta tell them you are bout to SI, but get them to talk to you... sometimes its best if they know you SI and understand it.  i always call my bestfriend who used to SI, she understands that she can't talk my emotions down but can support me.
GET OUT OF THE HOUSE!!  go for a drive, turn the radio up REAL LOUD and SING off pitch and awful... if you can't drive, go for a walk, sing and dance in the rain... be DUMB and CHILDISH!! 
play the 10 minute game.  say to yourself if i can wait ten minutes then i can SI, then once you hit the ten minutes say, if i went those ten minutes, lets try ten more.  it becomes a challange and we all love to challange ourselves. 
be with people.  if you have roommates, force yourself to watch tv, go out for ice cream (yummie), if you are at home with your parents, "bond with your mom or dad"  play with your younger siblings.  call a friend over.  get on the internet.  just try not to be alone.
ok, i know what you are saying, ok cassie, what you said is all fine and good, but its 1 am, no one is awake and i want to cut... now what.  first, check if im on line... i will put money that i am (i can never sleep) :) second, there are TONS of chat rooms for SI and depression.  try MSN or AOL  (im not familiar with AOL, but MSN you need a profile, so try it when you are safe for future help) i have gone to MSN a few times and people are GREAT! 
hold an ice cube REALLY hard in your hand, it hurts cause its sooo cold, or put a rubber band around your wrist and snap it...
for the future... i found that when i worked with a councelor we made a list of contacts, there are tons of hotlines that you can call, and some will open their lines to you.   we made a list of 4 people who could be called, two of which had to be adults (for a teenager) or professionals.  we also had a list of things to do when i was triggered, if these people couldn't be reached... i forgot to add clean up there... that was always on my list :) finally work to identify your triggers so you don't run into them again... most importantly if you are suicidal... CALL 911 PLEASE!!  you are too important in this world.  there is someone out there who cares, reach out!!
sometimes no matter how hard we try impulses are just too strong.  in this case (i know it sounds dumb) but try and control the damage.  cut as little as you can.  look for the light at the end of the tunnel... and remember, you tried.  there was probaly a point in your SI where you wouldn't have tried, so you are doing better and remember that you did try.  be proud of the avenues you travled and know there is a light at the end of the tunnel!