I know I'm late to the party, but since my battery is on the way out too I did some legwork:
Excellent battery 411:
http://home.mindspring.com/~jabrooks/
Possible replacements:
http://www.ibmwr.org/otech/partsubs.html
Best prices I found today, 11 Oct 06, in US-$ (all except noted include free ground shipping):
$70 Yakia 51913 sealed AGM battery, 230 cca (cold cranking amps), 12 mos warr, @
http://motorcyclebatteriesusa.com/batte ... attery=956
$70 Panasonic LCX-1220P, 20 AH, 18 mos warr, @
http://www.batteryweb.com
$48 + shipping Panasonic LCX-1220P (sealed lead-acid), 20 AH, 18 mos warr, @
http://www.digikey.com/
$92 WestCo 12V20P Sealed AGM 275 cca - 20 AH, 12 mos warr, @
http://www.ebatteriestogo.com/
$71 UPG UB22-12N Sealed AGM 420 cca - 22 AH, 12 mos warr, @
http://www.ebatteriestogo.com/
$68 Power Source WP20-12I Sealed AGM, 325 CCA - 20 AH, 12 mos warr, @
http://www.ebatteriestogo.com/
$ ? Yuasa 51913 19 AH, no other data on Yuasa site
$84 (plus s/h, e.g. to Fort Lauderdale FL $10) Odyssey PC680, 220 cca - 16 ah, 24 mos warr, @
http://www.batterystation.com/gelcell.htm
$76 (incl. or plus s/h? asked by email today) Odyssey PC680 @
http://www.batterygiant.com/Battery-Finder/?k=PC680
$78 (pickup or plus s/h, e.g. from Leesburg FL to Fort Lauderdale FL $19) Odyssey PC680 @
http://www.batteryweb.com/odyssey-detai ... odel=PC680
for comparison:
$106 Exide BMW-OEM 19 AH
I personally haven't quite made up my mind yet which battery it'll be. The Odyssey has less AHs but the longest warranty, which in Florida's battery-killing temps sure is an issue. Batteryweb also has a warehouse in N Miami, where I can pick it up and save the s/h, but that's obviously an exception.
PS on 9 Nov 06: bought a Panasonic for $51 incl. s/h at celltimebattery.com (which actually is a FedCoBattery site).