Pow! Bam! Interjections
I'm describing someone bumping into something and I want to use the interjection Bam! or Pow!
The closest I can find are ¡Pum! or ¡Bum! which seem to mean Bang! (as in from a gun or explosion)
Are there any more Batman-esque interjections in Spanish?
3 Answers
Crash: ¡¡Cataplúm!! catapún
Punches: paf, pum, pin-pam-pum, puf (in the stomach)
Explosions: bum, bam
Shots: bang, pum, ratatata (machine gun)
Crack: crac, cric, trac
wham bam: ¡Pum Pam!
More expressions for hits or sound of amazement, like on tv series like batman, superman etc:
Zas!, Pas!, Pum! Mocos! Riata! Pácatelas!
I have also seen ¡Plaf! and ¡Ploc! when someone hits someone else.
Hope some of those help 
Here's a link too that might give you some more ideas
Spanish Comic Strips
These are not interjections but onomatopeyas (onomatopoeias in English).
Perhaps this explanation might help:
Las onomatopeyas son palabras que a pesar de no reconocerlas, todos entendemos. Son transcripciones más o menos fieles de sonidos. Son onomatopeyas por lo tanto:
• ¡Tan, tan! Para describir el tañer de la campana,
• ¡Boom! Para una explosión …
Son muy abundantes en las viñetas; pueden estar o no dentro de globos y frecuentemente, van acompañadas de líneas cinéticas. Muchas de ellas provienen del inglés:
• Crack: quebrar, crujir.
• Splash: salpicar, chapotear.
• Click: sonar con uno o más golpes.
• Sniff: olfatear.
• Glup: engullir, tragar…
Here is a link where you can download a copy of un diccionario de onomatopeyas in MS-Word format.
However, from what I understand, the most extensive source on the subject is this book by Román Gubern that is over 400 pages long:
First thing that came to my mind was: Pum! ... I think you've found the best choice
