Check out Winters_SEO on youtube. He's got partial camo patterned Space Marines and they look brilliant.
About purple Marines... Soul Drinkers were loyal for awhile (may still be... I know they went renegade at a certain point, but they may have been exonerated). They look very solid.
I still think the Death Strike dudes look incredible. That dark Kantor Blue with the Y'riel Yellow markings looks absolutley incredible. For a simple recipe I'd base them Kantor Blue with a strong nuln oil wash... get them really dark and then just do a little clean up with Kantor and minimal highlights. Give them a blue-black type appearance with those bright yellow markings... I'm telling you it'd look ace!
I've done Pre-Heresy Emperor's Children and they look good... but not very intimidating unless you do a lot of weathering and really work those metallics with some interesting washes.
GW Blues are amazing and really easy to work with. I say Death Strike all the way. Sick colors, awesome name and easy paints to work with. Thats the holy trinity of hobby goodness!