OpenStreetMap offers quite a lot of options for linking to the maps. These are described on the documentation about browsing the map. To summarise with the example coordinates you gave, you can use a URL like
http://www.openstreetmap.org/?lat=30.486&lon=-90.195&zoom=16 ...to link to that location
http://www.openstreetmap.org/?mlat=30.486&mlon=-90.195&zoom=16 ...with a marker
http://osm.org/go/Tu_z5cFR ...as a 'short link' (redirects)
http://osm.org/go/Tu_z5cFR?m ...a 'short link' with marker
You can actually slap in a coordinate pair "30.486,-90.195" with a comma into the search box on the OpenStreetMap homepage, and that gives you a link to click, which dynamically zooms you to that spot, although you can also right click to open the link in a new window at a URL formatted as above.
If you want a frame embeddable map, check out the 'export tab' 'embeddable HTML' options documented here which gives you HTML like this:
<iframe width="425" height="350" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" src="http://www.openstreetmap.org/export/embed.html?bbox=-90.20224,30.48102,-90.18775,30.49097&layer=mapnik" style="border: 1px solid black"></iframe><br /><small><a href="http://www.openstreetmap.org/?lat=30.485995000000003&lon=-90.194995&zoom=15&layers=M">View Larger Map</a></small>
Contained with that is a URL like this...
All of these URL formats could be generated by Excel using a formula to go from the lat/lon values in two other cells.