So far, avocado has been the best (fortunately it's really really healthy!), but banana also works great. She's also liked really ripe fruit, particularly cantalope and watermelon (which is unfortunately just sugar and water, basically). I've also been able to give her cooked sweet potatoes in chunks and really soft boiled carrots in small chunks. I tried really small pieces of whole wheat toast too, which she seems to enjoy and manages well (I alternate it with something less dry or a sip of water). When we were at a family dinner recently, I gave her some vegetarian canneloni (spelling?) made with spinach and ricotta - she actually really enjoyed that too - she was over 9 months though, so I didn't mind giving her the dairy and the spinach. I just cut it into tiny pieces and I think the ricotta made it easier to move around in her mouth and swallow. That's all I can think of now!
When she gets fussy, I use Fruit Puffs (they're like cheerios but dissolve even faster). She knows the shape now, so if she starts to refuse food, I give her one to warm her up - works great!