The longtime champion map of Nicaragua is published by International Travel Map (ITM, www.itmb.com ), scaled at 1:750,000, colored to show relief, and with good road and river detail. They also offer an excellent Central America regional map. It’s found in many bookstores and travel shops, but not in Nicaragua.
A new favorite is produced by German cartographers Mapas NaTurismo (salsa_klaus [at] yahoo [dot] de, www.mapas-naturismo.com ). Their gorgeous 1:500,000 country map is water resistant and features detailed tourist attractions and natural reserves better than any other; it also has a few handy inserts, including Isla de Ometepe  at 1:200,000; samples available on their site and they are currently producing city maps of Masaya  and Granada , and a regional map of Managua  to Rivas . They go for about $7 at www.omnimap.com  or www.gotrekkers.com .
The Nelles Central America map (1:1,750,000) offers a quality overview of the region (plus more detail on Costa Rica) and is good if you are traveling the whole area and don’t intend to venture too far off the beaten track.
INETER, the Nicaraguan Institute of Territorial Studies, produces the only complete series of 1:50,000 maps (or topo quads) of Nicaragua, now available online at www.ineter.gob.ni . Produced in the 1960s and photo-revised in the 1980s with Soviet help, these are the most detailed topographical maps of Nicaragua that exist. They can be purchased from the INETER office in Managua (and occasionally at regional offices) for $3 each. The Managua office is located across from Policlinica Oriental and Immigration (tel. 505/2249-2768; open 8 a.m.–4:30 p.m. Mon.–Fri.).
Tactical Pilotage Charts (TPC K-25B and TPC K-25C) cover northern and southern Nicaragua, respectively, with some coverage of Costa Rica, Panamá, and Honduras at 1:500,000 scale. Designed for pilots, these maps have good representation of topography and are useful if you do any adventuring in the eastern parts of the country (far easier than carrying a stack of topo maps). Many smaller towns are shown, but only major roads.