Ibanez offers/has offered a couple of short-scale 5-strings. Woodcraft and Form Factor both offer 5s, though not inexpensive. I think Atelier Z does also.
Lots of makers are now offering short-scale 4-string basses. Fender/Squier offer various permutations of the Mustang and Musicmaster/Bronco from $200 on up, depending on your needs. If you like to tinker, buying a Bronco and dropping in a new pickup is a great way to go.
Other popular shorties: Gretsch, Sire, Ibanez on the lower end of the price scale. MusicMan recently jumped on the short scale bandwagon. If you're looking for a boutique instrument, yes, Serek and Birdsong. Also Warmoth, if you want to buy the parts and assemble yourself, or have a luthier do it. This allows you flexibility in configuration and materials.
Retrovibe (look on Reverb for his stuff) has some really cool models, and will probably do some customizing if you ask.
Gibson/Epiphone offer some, though you have to be careful because some models come in both short and long scale versions. Lots of folks have reported quality issues with the Epiphone Newports, though.
Feeling semi-hollow? The Guild Starfire is a terrific choice. I have a Starfire II and it sounds fabulous with flats.
Hollowbody with a vintage vibe, Epiphone Masterbilt is out of production but can be found used. It's also a terrific bass.
The Nordstrand Acinonyx (ak.a. "Cat") has been a real hit in the short scale community.
Acinonyx Short Scale Bass
It is about to go out of production, so if you want one you need to act fast. There's a thread devoted to these.
Is your head spinning yet?
