Home Runs in both "leagues": 30, 40, 50.

Data through 2015 from the Lahman database was manipulated using Microsoft Access. Some players played on multiple teams in the same year in the same league.

FirstName	LastName	MaxHRAL	MaxHRNL	ALyearFirst	ALyearLast	ALcount	NLyearFirst	NLyearLast	NLcount	ALteamFirst	ALteanmLast	NLteamFirst	NLteamLast
Adam	Dunn	41	46	2012	2013	2	2004	2010	7	CHA	CHA	CIN	CIN
Darrell	Evans	40	41	1985	1987	2	1973	1983	2	DET	DET	ATL	ATL
Shawn	Green	42	49	1998	1999	2	2001	2002	2	TOR	TOR	LAN	LAN
Ken	Griffey	56	40	1993	1999	6	2000	2007	3	SEA	SEA	CIN	CIN
David	Justice	41	40	1997	2000	2	1993	1993	1	CLE	CLE	ATL	ATL
Mark	McGwire	52	70	1987	1997	8	1998	2000	3	OAK	OAK	SLN	SLN
Albert	Pujols	40	49	2012	2015	2	2001	2011	11	LAA	LAA	SLN	SLN
Jim	Thome	52	47	1996	2008	10	2003	2004	2	CLE	CLE	PHI	PHI

Darrell Evans was the first to hit at least 40 Home Runs (HR) in both leagues. Adam Dunn and Albert Pujols are the most recent.

Obviously, Mark McGwire is the only player to hit at least 50 HR in both leagues. Not counted: McGwire hitting 58 HR in 1997: 34 for Oakland in the American and 24 for St. Louis in the National.

All 41 players with at least 30 HR in both leagues:

FirstName	LastName	MaxHRAL	MaxHRNL	ALyearFirst	ALyearLast	ALcount	NLyearFirst	NLyearLast	NLcount	ALteamFirst	ALteanmLast	NLteamFirst	NLteamLast
Dick	Allen	37	40	1972	1974	2	1966	1970	4	CHA	CHA	PHI	PHI
Tony	Batista	41	32	2000	2002	2	2004	2004	1	TOR	TOR	MON	MON
Jason	Bay	36	35	2009	2009	1	2005	2006	2	BOS	BOS	PIT	PIT
Adrian	Beltre	36	48	2011	2013	3	2004	2004	1	TEX	TEX	LAN	LAN
Bobby	Bonds	37	39	1975	1978	3	1969	1973	3	NYA	TEX	SFN	SFN
Ellis	Burks	32	40	2002	2002	1	1996	1999	3	CLE	CLE	COL	COL
Jeff	Burroughs	30	41	1973	1973	1	1977	1977	1	TEX	TEX	ATL	ATL
Miguel	Cabrera	44	34	2008	2013	6	2004	2007	3	DET	DET	FLO	FLO
Tony	Clark	34	30	1997	1999	3	2005	2005	1	DET	DET	ARI	ARI
Carlos	Delgado	44	38	1997	2004	8	2005	2008	3	TOR	TOR	FLO	FLO
Adam	Dunn	41	46	2012	2013	2	2004	2010	7	CHA	CHA	CIN	CIN
Jim	Edmonds	33	42	1995	1995	1	2000	2004	4	CAL	CAL	SLN	SLN
Darrell	Evans	40	41	1985	1987	2	1973	1983	2	DET	DET	ATL	ATL
Prince	Fielder	30	50	2012	2012	1	2007	2011	5	DET	DET	MIL	MIL
Troy	Glaus	47	37	2000	2006	4	2005	2005	1	ANA	ANA	ARI	ARI
Shawn	Green	42	49	1998	1999	2	2001	2002	2	TOR	TOR	LAN	LAN
Ken	Griffey	56	40	1993	1999	6	2000	2007	3	SEA	SEA	CIN	CIN
Vladimir	Guerrero	39	44	2004	2006	3	1998	2002	5	ANA	ANA	MON	MON
Frank	Howard	48	31	1967	1970	4	1962	1962	1	WS2	WS2	LAN	LAN
Raul	Ibanez	33	34	2006	2006	1	2009	2009	1	SEA	SEA	PHI	PHI
David	Justice	41	40	1997	2000	2	1993	1993	1	CLE	CLE	ATL	ATL
Dave	Kingman	35	48	1984	1986	3	1975	1982	4	OAK	OAK	NYN	NYN
Carlos	Lee	31	32	2003	2004	2	2005	2007	2	CHA	CHA	MIL	MIL
Greg	Luzinski	32	39	1983	1983	1	1975	1978	3	CHA	CHA	PHI	PHI
Fred	McGriff	36	37	1988	1999	4	1991	2002	5	TOR	TOR	SDN	SDN
Mark	McGwire	52	70	1987	1997	8	1998	2000	3	OAK	OAK	SLN	SLN
Larry	Parrish	32	30	1987	1987	1	1979	1979	1	TEX	TEX	MON	MON
Albert	Pujols	40	49	2012	2015	2	2001	2011	11	LAA	LAA	SLN	SLN
Mark	Reynolds	37	44	2011	2011	1	2009	2010	2	BAL	BAL	ARI	ARI
Frank	Robinson	49	39	1966	1973	4	1956	1965	7	BAL	BAL	CIN	CIN
Richie	Sexson	39	45	1999	2006	3	2001	2003	2	CLE	CLE	MIL	MIL
Gary	Sheffield	36	43	2004	2005	2	1992	2003	6	NYA	NYA	SDN	SDN
Reggie	Smith	30	32	1971	1971	1	1977	1977	1	BOS	BOS	LAN	LAN
Alfonso	Soriano	39	46	2002	2005	3	2006	2012	3	NYA	NYA	WAS	WAS
Dick	Stuart	42	35	1963	1964	2	1961	1961	1	BOS	BOS	PIT	PIT
Jim	Thome	52	47	1996	2008	10	2003	2004	2	CLE	CLE	PHI	PHI
Jason	Thompson	31	31	1977	1977	1	1982	1982	1	DET	DET	PIT	PIT
Greg	Vaughn	31	50	1993	1996	2	1998	1999	2	ML4	ML4	SDN	SDN
Robin	Ventura	34	32	1996	1996	1	1999	1999	1	CHA	CHA	NYN	NYN
Matt	Williams	32	43	1997	1997	1	1990	1999	5	CLE	CLE	SFN	SFN
Dave	Winfield	37	34	1982	1983	2	1979	1979	1	NYA	NYA	SDN	SDN

First 30/30: Dick Stuart.

Frank Robinson, Vladimir Guerrero, Richie Sexon and Alphonso Soriano were close to 40/40, missing by just one in one league.

David Justice hit 41 AL HR playing for Cleveland and the Yankees in 2000: 21/20.

Double digit figures in league counts:
Albert Pujols: all 11 seasons with St. Louis
Jim Thome: 10 AL seasons: Cleveland 7, White Sox 3

yearID	lgID	FirstOfnameFirst	FirstOfnameLast	CountOfteamID	MinOfteamID	MaxOfteamID	SumOfHR
1975	AL	Bobby	Bonds	1	NYA	NYA	32
1977	AL	Bobby	Bonds	1	CAL	CAL	37
1978	AL	Bobby	Bonds	2	CHA	TEX	31