Obsidian is an interesting character to play: although of little direct value in combat, she is the major "face" for the party (and indeed, she tends to think of the rest of the party as "her staff," regardless of how they may feel about that). Of course, as all good bards are, she's ready with buffs and backup healing. But interestingly enough, she's also the party wizard.
This is where she starts to actually get quite interesting. Obsidian has her Use Magic Device skill cranked way up (currently at +15, IIRC), which means she's got a 75% chance of using just about any wand, and certainly well over 50% of using any scroll or other interesting widget they might happen to come across. Which means that now, besides being the group's swiss army knife, she can also start getting blasty.
Blasty, blasty, blasty! ;)
She's never gonna outdo the single-target damage of sirfox's gunslinger or hantamouse's brute of a fighter/rogue, but hopefully she'll start being able to take out some of these clouds of mooks we find ourselves fighting from time to time. She's also going to start work on collecting a scrollcase full of useful oddball spells ("I've always wanted to use reckless infatuation!"), making her even more swiss army knifier.
This is going to be an expensive proposition at the start of things (wands cost hella money), but on the other hand she doesn't have much else to spend her money on. Magic weapons? What would be the point? Magic armor? Same deal. Her Str is 8-- anything heavier than her silky gossamer gown of mauve and she can't walk anyway. Her priciest pieces of adventuring gear are likely to be bracers of protection and some mnemonic vestments.
While thinking about all this, I happened upon Why Bards are Awesome by rpg_crank, which echoed quite a few things I'd already figured out, but also pointed out some interesting new ideas for me, such as the whole bard-with-a-whip thing.  (Interesting tidbit: whips can be finessed. She's looking at a level with no feat predetermined yet. Hmmmmm.)
My favorite bit from that post, and the part that sums up Obsidian best:
Remember, you are the one who tells everyone the tales of adventure. You figure prominently in every tale. Your name is the one that comes up the most in the songs. When people from far away hear about your party, they say "Aren't you 'Bard and Company'", not "Aren't you that adventuring group who contains a number of important people?" When you write the songs, THEY ARE YOUR LACKEYS.
Alas, I'm not going to get to play Obsidian again for weeks at the earliest, because this is the August From Heck. But I can at least have some fun thinking about her and, in a few stolen moments of off-time, maybe even write that story.
 So, yeah. She's a high charisma drow bard with a whip. How did I end up in this cliché of all things? O.o 
 Actually, I chose drow for her partially because I had some neat ideas about playing with her morally-ambiguous background, but mostly because she was based on Rarity from MLPFIM and I wanted her to have purple hair. Mechanically, she's a normal elf.