you see bleeding hearts in baskets alot
I usally just radomly mix anything under a foot and wait for the surprise

Geranium's , Impatients, and lots of other annuals. LOOK at annuals that could attract- Butterflies or Hummingbirds, for your mix.
You are the master gardener- thus it's up to you what you feel should be in them. Go for it.

happy spring.

I love impatiens and begonias...

I've been musing on this topic too. I like to play with simple combos of two plant types, such as:

One of these for trailing foliage...
- Vinca
- Ivy
- Helichrysum
- Dichondra

... and maybe one of these for blooms and a little extra sprawl:
- Dwarf morning glory
- Verbena
- Campanula
- Petunia
- Nasturtium
- Geranium
- ... darnit, there are a bunch of lovely plants whose names I don't remember offhand.

Did this last year, planning on it again: Blue Wave petunias and short yellow snapdragons.

Here is instructions on how to make the baskets I made last year with wave petunias:

http://www.carriespear.com/carrie/garden/annual/pages/hangingbaskets.html

You can see that they really grow like mad as the summer goes on!

Carrie