It is said that in Kaliyuga, beej mantra gives results quickly and that is the reason we see astrologers suggesting beej mantra more often than the Vedic mantra. I personally don't believe in this theory and believe that both of the mantras are equally effective. Though this post is about Beej mantra, so here are the mantras for each planet -
Sun (Surya)
Om hram hrim hraum sah suryaya namah
Moon (Chandra)
Om shram shrim shraum sah chandraya namah
Mars (Mangal)
Om kram krim kraum sah bhaumaya namah
Mercury (Budh)
Om bram brim braum sah budhaya namah
Jupiter (Guru)
Om gram grim graum sah gurave namah
Venus (Shukra)
Om dram drim draum sah shukraya namah
Saturn (Shani)
Om pram prim praum sah shanaisharaya namah
Rahu
Om bhram bhrim bhraum sah rahave namah
Ketu
Om sram srim sraum sah ketave namah