Search on ebay for Holox - there's a guy selling them one every half
hour or so. Watch out for the delivery charge though! Even so, you
should be able to pick one up for about £33 delivered, or a bit more if
you're impatient.

In my experience it's the best around - it works inside on the ground
floor, also works quite happily behind a coated windscreen under which
my old GPS unit used to fail completely. The built-in li-ion battery
lasts for 11 hours of use (I've personally used it for 9 hours without
recharge) and it charges with a standard mini-usb connector.

I've bought two (one for me and one for my wife) and my boss bought one
after seeing mine, as has (just this week) a friend of mine. It's
working with my old iPaq, my iMate SP5 smartphone and my new T-Mob Vario
II with no problems at all, TomTom sees it as just a standard Bluetooth GPS.

Time-to-first-fix in real-world terms is around 2 minutes, warm-start is
almost instantaneous (probably around 20 seconds).

Note however that the charging circuit is fairly picky - if you plug it
into eg a car USB charger that pushes out 12v or so it will charge but
the unit shuts off while it's charging (not helpful); I'm still unable
to find out if the car USB charger they sell separately (for £9, I
think) will solve this problem. It will stay on while charging from the
supplied (4.5v) mains charger, so I assume it's a voltage issue.

I've no idea about how good or otherwise is the software in the E61, sorry.

Geoff
No connection with Holox except as a very satisfied customer

Shaun has reviewed a Holux GPS receiver on his blog here:
<http://stmcgill.wordpress.com/2006/10/17/holux-gpslim240-gps-receiver-review-per
fect-add-on-for-the-e61/>

Seems to work perfectly with his E61.