i just bought my wife a mio digiwalker c220 ($129 from circuit city) and it performs all of the aforementioned tasks (custom waypoints, street navigation, etc.) and supports the lat/lon, mgrs, utm, loran td, and maidenhead grids. i also have an old magellan meridian handheld that i use on dual-sport motorcycle excursions and it doesn't do street nav, but it has map support and supports utm as well....you should be able to pick one of them up on ebay for a few bucks if you don't want to shell out the $$$ for a new mio (or whatever).

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1983 300D classic white 196,xxx
2007 toyota yaris lb
2007 nissan versa (wife's)
2001 nissan frontier
2006 bmw r1150gs
2001 ducati monster 900
2003 zr7s
2007 klr650