Some ideas:

Concept: DOSBox frontend / game launcher
It's great to be able to run old DOS games, but having to operate the DOS command line is not fun. A concept for a graphical frontend to it would be helpful. Configuring input and games should be as easy as with DrNokSnes (or maybe even easier?).

Concept: MPlayer or VLC mobile UI
An alternative video player with support for more formats. They exist to some degree, but there is really no UI for them yet. A concept for an UI to easily select videos, and control playback is what this session should yield.

Concept: Device-wide search
The idea is to have a simple way to search (via keyboard input) all data on the device - conversations, contacts, music, videos, documents, images, e-mails, notes, applications, ... Something like Gnome Do or Quicksilver, but for Maemo. Ideally, we would be able to replace the "type-to-search contacts" of the Desktop with this (but that's a technical issue, the idea is to get a concept for an easy-to-use device-wide search tool).

Usability: Nicotine (or any other P2P filesharing app)
There should be an easy way to search for files, download them and then play them back. Nicotine is already there, but there's too much configuration and clicking involved. I think Daniel would be happy to get some support here.

Usability: Dopewars
Improve the usability of Dopewars. Game sessions should automatically be saved and restored, trading and fighting should be easy, a better overview of the buy/sell lists, etc.. (while still retaining the original gameplay feeling.. or maybe not?). Dopewars is fun already, but the UI is lacking (try it out on Maemo 4).

Usability: irrecco
Last time I tried this, the UI was horrible (had to get the stylus out, but it was still hard to use). Still, it's (afaik) the only application that can currently make good use of the IR transmitter in the N900. The backend is available, all we now need is a beautiful and easy to use UI with which users can configure their remote control buttons.

Graphics: Panucci
This is a portrait and landscape audiobook / concert / DJ set / podcast player for Maemo (some use it for music, too). It supports bookmarks and resuming, so the UI focus should be on these features. The UI is currently not optimal, so graphic UI designs for both landscape and portrait mode would be nice. (Disclaimer: I'm a developer of Panucci)