Hmm, seems to fit here better than where I posted it. It's centred around Wolverhampton. Not being from Walsall I haven't done what was suggested above, nor have I done much East of Birmingham as I don't know the area extremely well.
http://bb.ohsk.net/uploads/railwaymap1.png
The basics:
Midland Metro line 2: use the Oxford-Worcester-Wolverhampton line (Wolverhampton to Dudley section) which, bar Oxford Way and slight other bits, is largely unbuilt on.
Heavy rail from Wolverhampton to Dudley.
Heavy rail from Dudley to Birmingham, via Halesowen, Old Hill, Longbridge.
Reopen the Harbourne Railway, serving areas of Edgbaston.
Camp hill line!
Castle Bromwich stations, curving around to Walsall via Aldridge.
More interchanges. Reopening Monmore Green station provides an interchange between the Metro and the Stour Valley line.
It's not great, but hey.
References:
http://www.railaroundbirmingham.co.uk/regional_map.php