Try whatever is good and has enough flavor to stand up to peanut butter.

Also consider using a small quantity of dried fruit if you can't find good fresh fruit.

Some people like apples on PB sandwiches. Personally, I don't, because it can be too watery... but go ahead and try it if you want. :)

I've tried strawberries as well, but that didn't taste so great..

I'm a huge peanut butter fan, and a huge fresh fruit fan, so I'm kind of biased. I tend to think the two go together in general. I like fresh strawberries sliced on peanut butter, a ripe pear, sliced apple, ripe peach slices, and that's about all I've tried so far. I'm curious to see if anyone else had different ideas.

I'd bet that frozen raspberries would be good!

I've done thin-sliced apples, too.  That's delicious, just slice them thinly and/or bite-sized pieces.   I've taken fresh ripe or thawed frozen berries (any kind or mixed) and mash them in a bowl with the back of a fork until the consistency you like.  You can add 1/2 to 1 teaspoon of sugar or honey if you need it, and it's still way under the cal count for 1 tablespoon of regular, non-sugar-free prepared preserves.  Spread it on top of your PB on your bread or mix with PB and then spread.  You can still have the payoff of PB&J but with lots more fruit and fiber and a lot less sugar.

Try raisins, like cass877 said, but also add a bit of cinnamon!

blueberries

mild subtle flavored fruits like plums, pears, apples, applesauce

edit: you can also make your own strawberry or any berry spread  Here's a start-Mash up berries (mm, strawberries).  Add some sweetener if you need it.  Let it sit for a few hours or over night.  Then, put pb on the bread.  Put the jelly on top of the pb so it doesn't soak the bread and then eat it like toast.

Peanut butter is lovely with raisins or with grapes... a lot of people like banana too. Or skip the bread altogether and put the peanut butter straight on a nice juice apple. Yum!

Ahh, well before all these suggestions came, I went out and bought some cherries and mangoes.  This morning I tried slicing up two and a half cherries and microwaved them over the peanut butter on the bread for about twenty seconds, and it was amazing!  I'm going to try the mango tomorrow. :3

And I'm not the biggest fan of raisins, so I had to skip taht option ^^;  And I don't think I have the tools to mash up the berries because I'm in temporary housing right now, without a lot of tools: just a few bowls, a knife, some measuring instruments, and a spoon.  And thanks for the suggestion kaji, but I love my bread too much! : D  So I'll stick with slices of fruit on my peanut butter sandwich :3

sometimes i take frozen raspberries and microwave them for about 15 seconds so they are kind of jam-like and thick, and then spread them like jam. i find raspberries are tart enough to stand up to pb.

hope this helps!

Oooo, I'll keep that in mind.  I'll look for raspberries at the supermarket next time I go =]

Haha...I definitely do not want to be sucked into the low-calorie sweeteners thing; I think I'll just stick with that as special treats.

By the way, the mango didn't turn out that well...next time I'll scope out the berries at the supermarket. =]