Taiwan hiking maps come in many shapes and forms, but with one common element - they're only in Chinese. The main printer of quality topographical maps is Sun River 上河. Their 1:25,000 TM__ series of 22 maps focusing on the top 100 peaks and key trails, plus a guide to mountain flowers and printed on weather/abuse-proof plastic is probably the most useful for hiking the high mountains. The accompanying hiking times and gradient charts seem accurate. Their 1:50,000 M__ (1-25) series seems to be out of print now with only certain maps still in stock, a pity as they covered some areas not on the TM__ series.
The M__ (40-47) series covers the hills around Taipei. M__ (31-36) follows an (often imaginary) "Green day hikes" route N-S over mid-level mountains and valleys just west of the main high mountains. Sun River also have a series of comprehensive Northern Taiwan hiking maps, and atlas-like books for all of Taiwan (1:50,000).
For regular navigation of Taiwan's roads, the free bilingual maps published by the Tourism Bureau are usually more than adequate. These are clear, marked with most appropriate places, and contain very few mistakes!!! In the collection there is a general Taiwan map, and separate maps dedicated to Northern Taiwan; Central Taiwan; Eastern Taiwan and Offshore Islands; and Southern Taiwan. The reverse is packed with lots of tourist information. Airports and tourist offices should have these - often you need to ask, failing that, politely suggest that they look in the bulging cupboard behind them.
Of interest to some hikers will be Sun River's coffee table map/photo books introducing the Top 100 peaks, and maps published by the forestry department for various excellent trails - why are these so hard to come by??? The Tourism Bureau's site has links to some good (and mediocre) maps. The Taiwan Mountain Magazine (pictured in first picture above) is a delight to look at even if you don't read Chinese. The googlemaps-based site CubePoint seems to work well. We are willing to annotate some maps with English, contact us at firstname.lastname@example.org
Richard Saunder's excellent Taipei day trips and Yangmingshan guides are available at the Community Services Center.
Of course Lonely Planet Taiwan (remember to get the most up to date edition) and the Rough Guide have lots of practical advice. Check out Lonely Planet author Robert's blog Pashan for great (and well written) Taiwan hiking suggestions.
Books not to do with hiking but worth noting: 'Private Prayers and Public Parades' by Mark Cantonhill. And 'Keeping up with the War God' by Steven Crook.
Let's not forget Taiwan's premier English-language bulletin board, Forumosa, for all sorts of information and sophisticated discussion.