The Nikon Coolpix 7900 only has 3x opt. Zoom.
By "good zoom" I thought you meant "superzoom".
If you want a nice little cam with 3x zoom - take a look at the Canon Ixus 50 (5 MP), the Casio Exilim Z750 (7 MP).
A good compromise in size and features between the Panasonic Lumix DMC-FZ5 and the above-mentioned smaller cams might be the brandnew Panasonic Lumix DMC-LZ2: 5 MP, 6x opt. Zoom, IS. Size: 100 mm x 64 mm x 33 mm