I'm recommending Martha Jones-centric fics all this week but they're not all Martha/Ten.
I'm starting with the longest story first - everything after this will be significantly shorter.
Story: For Old Time's Sake
Author's summary: Ace enters the TARDIS, mistaking it for her TARDIS and ends up going along with the Doctor, Martha, and Donna to Portsmouth in 1723.
Characters: Donna Noble, Dorothy (Ace) McShane, Martha Jones, The Doctor (10th), The Doctor (7th)
Word Count: 11790
Recced because: It's an action/adventure that seamlessly integrates Ace into the post-Season 3 Team TARDIS. I love the humour and banter that's shared between the four characters (especially Donna and Ace) and Seven's cameo is lovely too.
The Doctor’s voice trailed off when he saw the petite figure in the doorway. Head to toe in black. Hair pulled back from a cherub face, and the end of a baseball bat sticking out from the pack over her shoulder. "Ace?" Martha watched the myriad of emotions sweep across the Doctor's features and started for the doorway.
"No offence Gorgeous." Ace started, her usual cocksure attitude kicking in full force. "But I'd remember meeting you!" She smirked at the tall slender man staring at her. The look of initial shock on his face dissolving into one of bemusement as he held his hands out like scales.