The idea of competition is too broad. There are multiple levels to which current devices and platforms are competitive with Maemo 5 and the N900. Here's a small list (with the competitive areas)

The Archos Android Tablet - functionality, price, platform, web, multimedia
HTC Touch HD2 - functionality, price, platform, web
iPod Touch/iPhone - functionality, platform, multimedia, web, (price depending on region)
Nokia N97 - functionality, price, platform, web, multimedia
Palm Pre - platform, web
SE Xperia X2 - marketing, platform
Garmin nuvifone G60 - functionality
Asus/Acer/Dell/HP netbooks - functionality, platform, web

You can throw a ton of others in there. But again, competition happens on more than just raw numbers given by specs. Nokia cannot even make a product for sale until identifying these types of areas (in better detail than I have here). If this is a conversation to be had, we'd be better - for the community's sake - in making sure that we are realistic towards this topic, rather than fanboyish.