Whenever I run Blissey, I run fire blast anyway. But that's just me. She is setup fodder for you otherwise.
Alright guys, partners for DDMence gogogo.
Works best in rain or sun to outspeed weather pokes. Needs screen support because shit hits too hard. Needs a spinner because SR+LO=fail. And finally, it needs a way to tell scarf landorus to gtfo.
Okay, Salamence is probably better in sun since rain nerfs Fire Blast. If you run Roost over Fire Blast, it doesn't matter which weather you use. Magnezone is always a great partner, since it's got great typing synergy and traps the Steel-type Pokemon that give Salamence trouble.
For Rapid Spin, the standard options work just fine. Forretress is a good option because of its typing, so it can switch in on stuff like Scizor and Ferrothorn that Salamence lures in and start setting up hazards or get rid of them with Rapid Spin.
I personally don't think it really needs Reflect or Light Screen support as long as you're smart about switching it in and taking advantage of Intimidate, but having that support definitely helps. Any of the standard users of Reflect and Light Screen (Deoxys-S, Espeon, Bronzong, etc.) should work well.
If you try to use it outside of weather, you definitely need a way to get Excadrill out of the way. Skarmory or Bronzong can take it on pretty well and can also set up entry hazards that Salamence can take advantage of with all the switches it forces.
Anything that can lure Ground-type, Fighting-type, Grass-type, or Bug-type attacks for Salamence to switch into will probably make a pretty good partner. Trying to switch into Fire-type or Water-type attacks isn't such a good idea since as likely as not they're boosted by their respective weathers.
Wish support generally helps with Salamence's frailty and compensates for the residual damage Salamence usually takes. Jirachi resists all of Salamence's weaknesses and can pass 200 HP Wishes, while Blissey/Chansey and Vaporeon have huge HP stats and can lure some of the attacks that Salamence likes to switch into (Fighting-type and Grass-type attacks, respectively).