Thanks for all the inputs.
To sum it up and add a little bit of my research:
1. Smallest:
SB-30: Uses CR123A non-rechargeable Lithium batteries
2.3" x 3.3" x 1.4" 3.2 oz
GN: 52' at ISO 100 with 28mm
About $90
SB-50DX: Uses CR123 non-rechargeable Lithium batteries
Quite a bit bigger but small among the more powerful
2.5" x 4.2" x 4.1" 8.3 oz
GN: 72 in feet at ISO 100
About $160
SB-23: Not the smallest, but probably the smallest that uses 4xAA's
Designed in 1988
2.5" x 2.6" x 3.3" 4.9 oz
GN: 66' (ISO 100)
35mm coverage
About $90
2. Use AA's:
SB-23 see above (the smallest among AA Flashes)
SB-80DX - the latest and most powerful, a little bit too big for me.
Over $300
Other:
SB-27: Designed in 1995
4 x AA's
2.8" x 4.2" x 3.8" 12 oz
GN: 98'
24mm Coverage
About $180
SB-22S: Designed in 1998
4 x AA's
4.1" X 2.7" x 3.1" 7.4 oz
GN: 92'
28mm coverage
About $140
3. Other Flash units - Universal application?
Sunpak 355AF: Uses 4xAA's, it seems to have versions (different
shoe mounts?) for Canon, Nikon, Minolta, Pentax, .... How does it
work? Can you get one Flash unit say for Nikon (CP5000) at about
$70, then get an additional but different shoe mount (at say $10 to
$20?) say for Canon and the Flash unit can also be used for Canon
G2 or G3? Or those were just for film cameras. For digicams, any
one version would fit the other digicam? Sunpak 355AF seems to have
3-position manual zoom (35/50/85mm), how would the 35mm zoom do for
CP5000 at 28mm?
Canon 220 Ex: - use AA's
2-9/16in. (W) x 3-5/8in. (H) x 2-7/16in (D) 5.6 oz
GN: 72' (ISO 100)
28/24mm coverage
About $140
I am thinking about getting 220Ex for Canon G2/Pro90. Can it also
be used with CP5000 with limited functions?
Or can any of the Nikon SB flash use for Canon G2/Pro90? Which is
the better way to go?
Right now, I am considering SB-30, SB-23 or SB-22S (more compact
and the latter two can use AA's) for the Nikon. Will also consider
the Sunpak 355AF when I learn more about it.
Thanks in advance for more comments to help me decide.