Alright so my lock will be 60 very soon

[Arnath]

I'm going to agree with Icebird and say that you should go either 7/21/21+2, or, if you really like destruction, give NF/Conflag a try. I don't particularly like MD/Ruin builds, particularly for soloing/pvp-ing because the lack of improved lifetap and instacast Corruption is really annoying. 7/21/21+2 is a great soloing/raiding/instancing build because you get a LOT of utility out of Demonic Sacrifice. It lets you adapt to all sorts of situations (I don't personally really like the build, but that's beside the point). I've been told NF/Conflag is a lot of fun, although I've never tried it myself. Basically, I'd suggest the 7/21/21+2 build.