bands like hollywood undead and mindless self indulgence?

Hollywood Undead and Mindless Self Indulgence are pretty different, but I do like both of them. You might want to check out System of a Down, 3OH!3, The Offspring, Linkin Park, and maybe Jon Bon Jovi. Defienetely check out Starstrukk and Can't Do It Alone by 3OH!3. I love them.

Err,
those bands are [very] different from each other.
But if you like MSI, you'll like:
Sky eats airplane
The dillinger escape plan
Enter Shikari
The fall of troy.
^ Those are "Mathcore" bands, but they have an electric touch to them like MSI.
You might also like some hardcore punk,or bands such as Run Kid Run or NOFX.

I haven't heard Hollywood Undead... No wait... I've heard one song. But anyway.

Tryyy...
Rabbit Junk
Ayria
Apoptygma Berzerk
Faderhead
VNV Nation
The Birthday Massacre
Leæther Strip

Okay they aren't really that similar to MSI, but still...

Edit: Re-ordered it. I think Rabbit Junk are the closest.