Other Sharpe-like books?

The only thing I was going to suggest was O'Brien and I see that's covered. Not many other's like those two unless you go back a few decades and then the style is less than modern.

Perhaps...

these titles recommended by the reviewers in the November Historical Novel Society Review? They are all newly published in 2006.

'Jack Absolute' by CC Humphreys, St Martin's Press - a rollicking adventure set against the American Revolutionary war.

'A King's Trade' by Dewey Lambdin, St Martin's Press - a Napoleonic wars navel adventure

Any of the Kydd series by Julian Stockwin - McBooks
Another Napoleonic wars naval series. These have been getting rave reviews.
6th title is 'Tenacious'.

'St Patrick's Battalion' by James Alexander Thom, Ballantine - the American Mexican war.

Just maybes:
'Brothers' by Da Chen - two very different lives in Communist China, one brother is a bastard, and the events of Tiananmen Square.

The Awakening series by Bill Bright

Oh, and if your brother likes spy/murder adventure mysteries then any of Michael Pearce's Mamur Zapt books are very funny, very clever and set in British Colonial Egypt. I recommend 'A Touch of Ice' as a first taste.

CS Forrester's Hornblower series? A few decades old, but I think they've aged well

Cornwell"s "Starbuck chronicles" - American Civil War!

If your brother would be interested in military SF, I'd suggest the following:

Lois McMaster Bujold's Miles Vorkosigan series (starts with Shards of Honor)

David Webber's Honor Harrington series (starts with On Basilisk Station)

Eric Flint and David Drake - the Belisarius series (starts with An Oblique Approach)

If he likes O'Brien, he might like Alexander Kent's Richard Bolitho series.

Definately Hornblower.